Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device. The secondary battery comprises a casing. The casing defines an accommodating cavity. The casing comprises a first wall portion. The first wall portion comprises a first wall surface facing away from the accommodating cavity and a second wall surface facing the accommodating cavity. The first wall portion is provided with a first through hole running through the first wall surface and the second wall surface. The secondary battery further comprises a pressure relief assembly. The pressure relief assembly comprises a metal piece and a sealing member. In a direction from the second wall surface to the first wall surface, the metal piece comprises a first metal layer and a second metal layer that are stacked. The sealing member is bonded between the first metal layer and the first wall surface. The metal piece covers the first through hole. The coefficient of thermal expansion of the first metal layer is G1. The coefficient of thermal expansion of the second metal layer is G2. The following condition is met: G1>G2. The present application facilitates a timely response to a change in an internal temperature of the secondary battery, and implements timely pressure relief of the secondary battery, thereby reducing the risk of explosion of the secondary battery.

Description

Secondary batteries and electronic devices

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202411911116.0, filed on December 24, 2024, entitled “Secondary Battery and Electronic Device”, the entire contents of which are incorporated herein by reference.

[0003] Technical Field

[0004] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0005] With the rapid development of new energy technologies, batteries have been widely used in mobile phones, laptops, electric vehicles, and other fields, and the requirements for battery quality and safety are becoming increasingly stringent. However, batteries are prone to thermal runaway when exposed to high temperatures or short circuits, causing the internal gas pressure to gradually increase, which can lead to fire or even explosion, posing a safety risk. Summary of the Invention

[0006] One objective of this application is to provide a secondary battery and electronic device to reduce the technical problem that secondary batteries are prone to explosion.

[0007] In a first aspect, embodiments of this application disclose a secondary battery, including a housing that encloses a receiving cavity. The housing includes a first wall portion, which comprises a first wall surface facing away from the receiving cavity and a second wall surface facing the receiving cavity. The first wall portion has a first through hole penetrating the first wall surface and the second wall surface. The secondary battery also includes a pressure relief assembly, which includes a metal sheet and a sealing element. 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 element is bonded between the first metal layer and the first wall surface, and the metal sheet covers the first through hole. The coefficient of thermal expansion of the first metal layer is G1, and the coefficient of thermal expansion of the second metal layer is G2, where G1 > G2.

[0008] In the above technical solution, a bimetallic shape memory alloy sheet is formed by utilizing the difference in the thermal expansion coefficients of the two metal layers. Because the thermal expansion coefficient of the first metal layer is greater, when the secondary battery experiences an abnormal situation that causes the temperature to rise, the first metal layer expands more, causing the edge of the first metal layer to bend and lift towards the second metal layer. This leads to the first metal layer partially detaching from the seal, weakening the adhesion between the metal sheet and the seal, making it easier for the seal to be opened. This allows for the timely release of internal pressure in the secondary battery, thus playing a role in pressure relief.

[0009] Compared to traditional pressure relief components, the bimetallic shape memory alloy in this embodiment is more sensitive to temperature changes and can respond promptly to temperature variations within the secondary battery. This helps to release gas in a timely manner, reducing the risk of a rapid increase in internal pressure and effectively lowering the risk of explosion. Furthermore, the shape memory properties of the bimetallic shape memory alloy allow the metal sheet to return to its original state after cooling, enabling it to re-engage with the sealing component to restore the battery's seal and facilitating the reuse of the pressure relief component.

[0010] In some embodiments, the thickness of the metal sheet along the direction from the first wall surface to the second wall surface is D1, where 0.04mm ≤ D1 ≤ 1mm. This facilitates the normal use of the secondary battery under normal operating conditions and enables timely response to temperature changes in the secondary battery, as well as timely pressure relief in abnormal situations.

[0011] In some embodiments, the thickness of the first metal layer is D along the direction from the first wall surface to the second wall surface. 11 The thickness of the second metal layer is D. 12 , 1≤D 11 / D 12 ≤5. This reduces excessive bending of the metal sheet, which is beneficial for the normal use of the secondary battery under normal operating conditions. At the same time, it can respond promptly to temperature changes in the secondary battery, which is beneficial for timely pressure relief in abnormal situations.

[0012] 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. This allows the metal sheet to operate normally within the normal temperature range (generally -20°C to 85°C) and deform at temperatures between 90°C and 150°C. For example, the metal sheet may use a copper-nickel-chromium-iron combination, a copper-zinc alloy-manganese-copper-nickel combination, or a copper-tin-zinc-Invar alloy combination, all of which have deformation temperatures between 90°C and 150°C, which is beneficial for the timely pressure relief of the secondary battery.

[0013] In some embodiments, the metal sheet further includes a third metal layer, which is stacked between the first and second metal layers. During battery manufacturing, the metal sheet undergoes heat treatment. Due to the different coefficients of thermal expansion of the two metal layers, deformation is likely to occur during heat treatment. The third metal layer acts as a buffer, reducing the risk of deformation and separation of the metal layers caused by excessive local stress. Furthermore, the regulating effect of the third metal layer on heat conduction helps optimize the response speed and accuracy of the pressure relief component. More uniform and timely heat conduction allows the metal sheet to deform rapidly when the internal temperature of the secondary battery reaches a set value, opening the pressure relief channel. The third metal layer may be made of pure nickel, pure copper, or zirconium copper. Pure nickel, pure copper, or zirconium copper have good toughness and thermal conductivity, which is beneficial for stress dispersion and timely heat transfer.

[0014] In some embodiments, the coefficient of thermal expansion of the third metal layer is G3, where G2 < G3 < G1. This can better alleviate the stress caused by the first and second metal layers and reduce the risk of metal sheet deformation.

[0015] In some embodiments, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃. This is beneficial for the normal use of the secondary battery and can respond promptly to temperature changes, facilitating timely pressure relief in abnormal situations.

[0016] In some embodiments, the pressure relief assembly further includes a connecting piece disposed on the first wall surface. The connecting piece has a second through hole communicating with the first through hole. A seal is bonded between the connecting piece and the first metal layer, and a metal sheet covers the second through hole. During installation, the seal can be bonded between the metal sheet and the connecting piece first, and then the connecting piece can be connected to the housing, simplifying the installation process and improving installation accuracy. During disassembly, the entire pressure relief assembly can be detached from the housing by separating the connecting piece from the housing, ensuring high integrity of the pressure relief assembly and facilitating its reuse.

[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 stacked together. A second through-hole penetrates the fourth and fifth metal layers, 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 G4, and the coefficient of thermal expansion of the fifth metal layer is G5, where G4 > G5.

[0018] Because the fourth metal layer has a higher coefficient of thermal expansion, it expands more when the secondary battery experiences an abnormal condition that causes a temperature rise. Due to the constraint of the first wall, the central portion of the fourth metal layer protrudes away from the first wall, causing it to detach from the seal. This weakens the adhesion between the connecting piece and the seal, making it easier for the seal to be opened and thus releasing the internal pressure of the secondary battery in a timely manner, effectively relieving pressure. Furthermore, the opposite bending direction of the connecting piece and the metal piece further reduces the bonding area between the seal, the metal piece, and the connecting piece, further weakening the adhesion. This improves the sensitivity of the pressure relief assembly, enabling it to respond promptly to abnormal temperature changes in the secondary battery.

[0019] In some embodiments, viewed along the direction from the first wall surface to the second wall surface, the connecting piece includes a first portion overlapping the first wall portion. The first portion includes a first region fixed to the first wall portion and a second region not fixed to the first wall portion. The first region surrounds the second region, and the second region surrounds the first through hole. Only the first region of the connecting piece near the edge is fixed to the housing, while its central portion is relatively free. This structural design provides a certain degree of flexibility for the pressure relief assembly. When the internal pressure of the secondary battery changes, since the central portion of the connecting piece is not fixed, it can better adapt to the outward bulging deformation of the center of the connecting piece, which is beneficial for timely pressure relief when the gas pressure increases or the temperature changes.

[0020] In some embodiments, viewed along 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, the second portion covering a portion of the first through hole. When the pressure inside the housing increases, the gas can impact a portion of the second portion of the connecting piece, which is more conducive to the second portion driving the second area to bulge in a direction away from the housing, thereby causing the connecting piece to separate from the sealing portion.

[0021] In some embodiments, the width of the first region is W1, 0.1mm≤W1≤1mm, and the width of the second region is W2, 1 / 10≤W1 / W2≤1 / 3. This allows the secondary battery to have better sealing performance under normal operating conditions and facilitates the second region to bulge away from the first wall under abnormal operating conditions, making it easier to open the seal and allowing for timely pressure relief of the secondary battery.

[0022] In some embodiments, when viewed along the direction from the first wall surface to the second wall surface, the connecting piece is annular, and the outer diameter of the connecting piece is R, where 1mm ≤ R ≤ 6mm. This can reduce the impact on the energy density of the secondary battery and allow the connecting piece and the seal to have sufficient connection area, reducing the possibility of the connecting piece loosening or falling off and improving the reliability of the pressure relief assembly. Preferably, in some embodiments, 2mm ≤ R ≤ 5mm.

[0023] In some embodiments, the diameter of the first through hole is R1, 0.5≤R1≤5.5mm, which not only reduces the entry of external air and moisture into the secondary battery, but also facilitates the timely discharge of gas. The diameter of the second through hole is R2, 0.1mm≤R2≤4mm, which not only reduces the entry of external air and moisture into the secondary battery, but also reduces the risk of the second through hole being blocked, and further facilitates the timely discharge of gas.

[0024] In some embodiments, when viewed along the direction from the first wall surface to the second wall surface, the area of ​​the first through hole is S1, the area of ​​the second through hole is S2, S2 < S1, and 0.00785 mm. 2 ≤S2≤16mm 2 This allows the connecting piece to limit the contact between external substances and the electrolyte and electrode materials inside the secondary battery, enabling the chemical reactions inside the secondary battery to take place in a relatively stable environment.

[0025] In some embodiments, the pressure relief assembly further includes a protective layer disposed on the surface of the second metal layer opposite to the first metal layer. The protective layer can act as a buffer layer to absorb and disperse these external forces, reduce scratches, deformation, or breakage of the metal sheet, and improve the stability of the shape and performance of the metal sheet.

[0026] In some embodiments, the thickness of the metal sheet along the direction from the first wall to the second wall is D1, where 0.01 mm ≤ D1 ≤ 0.25 mm. A thinner metal sheet results in a shorter heat conduction path, allowing heat to be transferred more quickly within the metal sheet when the internal temperature of the secondary battery changes. This enables the bimetallic shape memory alloy sheet to sense temperature changes and respond more rapidly.

[0027] In some embodiments, the thickness of the protective layer along the direction from the first wall surface to the second wall surface is D2, where 0.01mm ≤ D2 ≤ 0.25mm. This provides effective protection for the metal sheet and facilitates timely deformation of the metal sheet under temperature changes. Preferably, 0.01mm ≤ D2 ≤ 0.15mm.

[0028] In some embodiments, the protective layer is made of at least one of polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate, or polyetheretherketone. Each material possesses a certain strength and toughness, enabling it to withstand certain external forces and providing excellent protection for the metal sheet.

[0029] In some embodiments, the melting point of the seal is T, where 90°C ≤ T ≤ 150°C. Within the normal operating temperature range of the secondary battery, the seal exhibits excellent sealing performance, effectively sealing 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, allowing the pressure relief assembly to open promptly and reducing the risk of excessive internal pressure and potential explosion within the secondary battery.

[0030] In some embodiments, the thickness of the seal is D3 along the direction from the first wall surface to the second wall surface, where 0.01mm ≤ D3 ≤ 0.5mm. This can improve the sealing performance under normal operating conditions of the secondary battery and can promptly open the pressure relief channel in case of abnormal secondary battery conditions.

[0031] In some embodiments, the material of the seal includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, or polytetrafluoroethylene.

[0032] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0033] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0034] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0035] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0036] Figure 2 is a schematic diagram of the explosion of a secondary battery according to some embodiments of this application;

[0037] Figure 3 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0038] Figure 4 is a schematic diagram of the structure of a pressure relief assembly (pressure relief state) according to some embodiments of this application.

[0039] Figure 5 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0040] Figure 6 is a schematic diagram of the explosion of a secondary battery according to some embodiments of this application;

[0041] Figure 7 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0042] Figure 8 is a structural schematic diagram of a pressure relief assembly (pressure relief state) according to some embodiments of this application.

[0043] Figure 9 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0044] Figure 10 is a schematic diagram of the structure of a pressure relief assembly (pressure relief state) according to some embodiments of this application.

[0045] Figure 11 is a structural schematic diagram of a pressure relief assembly (pressure relief state) according to some embodiments of this application.

[0046] Figure 12 is a front view of a secondary battery according to some embodiments of this application (viewed along the direction perpendicular to the first wall).

[0047] Figure 13 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0048] Figure 14 is a schematic diagram of the structure of a pressure relief assembly (pressure relief state) according to some embodiments of this application.

[0049] Figure 15 is a partial structural schematic diagram of a secondary battery according to some embodiments of this application;

[0050] Figure 16 is a schematic diagram of the structure of a pressure relief assembly according to some embodiments of this application;

[0051] Figure 17 is a schematic diagram of the stacked structure of metal sheets and protective layers in some embodiments of this application.

[0052] Explanation of reference numerals in the attached figures:

[0053] 100. Secondary batteries;

[0054] 10. Shell; 10a. Main body; 10b. Cover; 11. Receiving cavity; 12. First wall; 121. First wall surface; 122. Second wall surface; 123. First through hole;

[0055] 20. Electrode assembly;

[0056] 30. Pole post;

[0057] 40. Pressure relief assembly;

[0058] 41. Metal sheet; 411. First metal layer; 412. Second metal layer; 413. Third metal layer;

[0059] 42. Sealing element; 421. Third through hole;

[0060] 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;

[0061] 44. Protective layer;

[0062] X, the first direction; Y, the second direction. Embodiments of the present invention

[0063] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0064] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0065] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0066] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0067] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0068] In a first aspect, this application proposes a secondary battery 100. Referring to Figures 1 and 2, the secondary battery 100 includes a housing 10, an electrode assembly 20, a terminal post 30, and a pressure relief assembly 40. The electrode assembly 20 is disposed within the housing 10. One end of the terminal post 30 is connected to the electrode assembly 20, and the other end protrudes from the housing 10. The terminal post 30 is used to lead out one polarity of the secondary battery 100. The pressure relief assembly 40 is disposed within the housing 10. When the gas pressure inside the housing 10 is high, the pressure relief assembly 40 can release some of the gas inside the housing 10.

[0069] Referring to Figure 2, the housing 10 encloses a receiving cavity 11, which can accommodate the electrode assembly 20 and the electrolyte (not shown in the figure). The electrolyte wets the electrode assembly 20 in the receiving cavity 11, thereby causing an electrochemical reaction. In the embodiments of this application, the housing 10 can be formed by stamping a conductive metal layer. The thickness of the conductive metal layer can be set to 0.1 mm to 0.4 mm, so that the housing 10 has high stamping strength.

[0070] The conductive metal layer can be made of materials such as aluminum, steel, stainless steel, nickel, copper or magnesium alloy, which allows the casing 10 to lead out one polarity of the secondary battery 100, while the aforementioned terminal 30 can lead out the other polarity.

[0071] The housing 10 can be square, trapezoidal, or cylindrical, etc., taking a square housing 10 as an example. In some embodiments, referring to Figures 1 and 2, the housing 10 includes a main body 10a and a cover 10b. The main body 10a is provided with a cavity, and one end of the main body 10a is open, allowing the electrode assembly 20 to be directly placed in the cavity through the open end. The cover 10b is connected to the main body 10a and covers the cavity, thereby forming a receiving cavity 11.

[0072] Referring further to Figure 3, the housing 10 includes a first wall portion 12, which 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 has a first through hole 123, which penetrates the first wall surface 121 and the second wall surface 122, and communicates with the receiving cavity 11. When the gas pressure inside the housing 10 increases, some gas can be discharged outward through the first through hole 123, reducing the risk of explosion of the secondary battery 100. The first through hole 123 can also serve as an injection hole. During the assembly of the secondary battery 100, after the cover 10b is connected and sealed to the main body 10a, electrolyte can be directly injected into the receiving cavity 11 through the first through hole 123, facilitating the preparation of the secondary battery 100.

[0073] The electrode assembly 20 is disposed in the receiving cavity 11 of the housing 10. The shape of the electrode assembly 20 can be configured to fit the housing 10 so as to make full use of the space of the receiving cavity 11 of the housing 10 and improve the energy density of the secondary battery 100.

[0074] The electrode assembly 20 includes a positive electrode (not shown), a negative electrode (not shown), and a separator (not shown). The positive electrode, separator, and negative electrode are stacked and wound together to form a wound electrode assembly 20. Alternatively, several positive electrode pieces and several negative electrode pieces are stacked alternately, with a separator between adjacent positive and negative electrode pieces to form a stacked electrode assembly 20.

[0075] The negative electrode of the electrode assembly 20 can be directly electrically connected to the housing 10, so that the housing 10 leads out the negative electrode. The positive electrode of the electrode assembly 20 can be electrically connected to the electrode post 30, so that the electrode post 30 leads out the positive electrode. In some other embodiments, the housing 10 can also lead out the positive electrode, and the electrode post 30 can lead out the negative electrode.

[0076] Referring to Figures 1 and 2, the electrode post 30 is disposed on the first wall portion 12. A portion of the electrode post 30 is electrically connected to the electrode assembly 20 within the receiving cavity 11, while the other portion protrudes from the first wall portion 12. In the embodiments of this application, the polarity of the electrode post 30 is opposite to that of the housing 10. An insulating member (not shown in the figures) can be provided between the electrode post 30 and the housing 10 to reduce short circuits. The insulating member can also be bonded between the electrode post 30 and the first wall portion 12, which on the one hand connects the electrode post 30 and the housing 10, and on the other hand seals the installation gap between the electrode post 30 and the housing 10, thereby improving the sealing performance of the secondary battery 100.

[0077] Referring to Figures 2 and 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, thereby improving the sealing performance of the housing 10.

[0078] When the secondary battery 100 is in a high-temperature environment or experiences a short circuit, it is prone to thermal runaway. The internal pressure of the casing 10 gradually increases and impacts the metal sheet 41 and the seal 42, which can cause the seal 42 to be forced open, thereby forming a pressure relief channel connecting the receiving cavity 11 to the outside, which can reduce the risk of the secondary battery 100 exploding. The seal 42 may also be provided with a third through hole 421, which communicates with the first through hole 123, to facilitate the pressure relief by forcing open the seal 42.

[0079] However, the inventors of this application have found that it takes a long time and a large gas pressure for the gas inside the housing 10 to break through the seal 42. If the gas pressure of the housing 10 rises rapidly in a short period of time, the pressure relief component 40 may not be able to respond in time, and there is also a risk that the secondary battery 100 may explode.

[0080] To mitigate the aforementioned problems, in the embodiments of this application, the metal sheet 41 may be made of a bimetallic shape memory alloy. Referring to Figures 3 and 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 together. The sealing member 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. The coefficient of thermal expansion of the first metal layer 411 is G1, and the coefficient of thermal expansion of the second metal layer 412 is G2, where G1 > G2.

[0081] In the embodiments of this application, the metal sheet 41 of the bimetallic shape memory alloy utilizes the difference in thermal expansion coefficients of the two metal layers to achieve its function. Under normal temperature, the metal sheet 41 maintains a certain shape, cooperates with the seal 42, and together maintains the sealed state of the secondary battery 100. When an abnormality occurs inside the secondary battery 100, such as overcharging or short circuit, causing the temperature to rise, the metal sheet 41 will change shape due to the temperature change.

[0082] In the embodiments of this application, because the first metal layer 411 has a larger coefficient of thermal expansion, when the secondary battery 100 experiences an abnormal situation that 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 towards the second metal layer 412, thereby causing the first metal layer 411 to partially detach from the seal 42. This weakens the adhesion between the metal sheet 41 and the seal 42, making it easier for the seal 42 to be opened, thus realizing the timely release of internal pressure in the secondary battery 100 and playing a timely pressure relief role.

[0083] Compared to traditional pressure relief components, the bimetallic shape memory alloy in this embodiment is more sensitive to temperature changes and can respond promptly to temperature changes inside the secondary battery 100. This helps to release gas in a timely manner and reduces the risk of explosion caused by a rapid increase in internal pressure of 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 shape memory alloy reacts quickly and can open the pressure relief channel earlier than pressure relief components 40 made of ordinary materials.

[0084] Furthermore, the shape memory properties of the bimetallic shape memory alloy allow the metal sheet 41 to return to its original state after the temperature drops. For example, if the abnormal situation inside the secondary battery 100 is resolved and the temperature drops, the metal sheet 41 of the bimetallic shape memory alloy will return to its original state and can, to a certain extent, cooperate with the seal 42 again to restore the sealing state of the secondary battery 100, which is beneficial for the reuse of the pressure relief component 40.

[0085] Both the electrode post 30 and the pressure relief assembly 40 can be located in the first wall portion 12. There is a large space between the electrode post 30 and the electrode assembly 20, which is conducive to the exhaust and pressure relief of the pressure relief assembly 40.

[0086] For measuring the coefficient of thermal expansion of a metal layer, a dilatometer can be used. First, a rectangular sample is prepared, ensuring its surface is smooth and defect-free. A dilatometer is used, and the equipment is calibrated to ensure measurement accuracy. The sample is placed in the dilatometer and tested under controlled temperature conditions. The temperature is changed slowly and uniformly, and the dimensional changes of the sample are measured. During the temperature change, the dilatometer records the length change of the sample, recording the length change data at different temperatures. The linear coefficient of thermal expansion, G = ΔL / (L0 × ΔT), is calculated using the formula, where ΔL is the length change, L0 is the initial length, and ΔT is the temperature change.

[0087] In the embodiments of this application, referring to Figure 3, along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the thickness of the metal sheet 41 is D1, 0.04mm≤D1≤1mm. This facilitates the normal use of the secondary battery 100 under normal operating conditions, giving the secondary battery 100 better sealing performance; and it can respond promptly to temperature changes in the secondary battery 100, reducing the opening or closing of the pressure relief component 40 at inappropriate temperatures, which is beneficial for the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0088] Regarding the thickness ratio of the first metal layer 411 to the second metal layer 412, if the ratio is too large, the first metal layer 411, with its higher coefficient of thermal expansion, will be even thicker. This could lead to excessive bending of the metal sheet 41, causing stress concentration. During deformation caused by temperature changes, significant stress may be generated at the interface between the first metal layer 411 and the second metal layer 412, potentially causing cracks or delamination in the metal sheet 41. This would affect the service life of the pressure relief assembly 40 and hinder its reuse. Furthermore, an excessively large thickness ratio could cause the metal sheet 41 to bend even with slight heating, potentially affecting the normal operation of the secondary battery. Conversely, if the thickness ratio is too small, meaning the first metal layer 411 is thinner, its expansion or contraction during temperature changes will be less pronounced. This could make it difficult to deform the second metal layer 412 and open the pressure relief channel, increasing the risk of explosion.

[0089] In the embodiments of this application, the thickness of the first metal layer 411 is D along the direction from the first wall surface 121 to the second wall surface 122 (first direction X). 11 The thickness of the second metal layer 412 is D. 12 , 1≤D 11 / D 12≤5. It can reduce excessive bending of the metal sheet 41, which is beneficial to the normal use of the secondary battery 100 under normal working conditions. It can also reduce the occurrence of cracks or delamination of the metal sheet 41 due to excessive bending. At the same time, it can respond to the temperature changes of the secondary battery 100 in a timely manner, which is beneficial to the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0090] In the embodiments of this application, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃, when the difference in the thermal expansion coefficients of the two metal layers is less than 4×10 -6 At a temperature of / ℃, the deformation of the metal sheet 41 during temperature changes is relatively small. When the internal temperature of the secondary battery 100 rises, the deformation of the metal sheet 41 may not be sufficient to quickly and effectively open the pressure relief channel, resulting in the internal pressure of the secondary battery 100 not being released in time, increasing the safety risk of the secondary battery 100 under abnormally high temperatures. Furthermore, the difference in thermal expansion coefficients is greater than 15×10⁻⁶. -6 At temperatures below a certain temperature, the metal sheet 41 becomes more sensitive to temperature fluctuations. Even small temperature fluctuations can cause significant deformation of the metal sheet 41, which may interfere with the normal sealing of the secondary battery 100 under normal operating conditions. (Limited to 4×10) -6 / ℃≤G1-G2≤15×10 -6 / ℃, which is beneficial to the normal use of the secondary battery 100 and can respond to the temperature changes of the secondary battery 100 in a timely manner, and is conducive to the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0091] The first metal layer 411 is made of at least one of the following materials: nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy, or alloy steel. The second metal layer 412 is made of at least one of the following materials: nickel-iron alloy, Invar alloy, nickel-chromium-iron, or manganese-copper-nickel. This allows the metal sheet 41 to operate normally within the normal temperature range (generally -20℃ to 85℃) and deform at temperatures between 90℃ and 150℃. For example, if the metal sheet uses a copper-nickel-chromium-iron combination, a copper-zinc alloy-manganese-copper-nickel combination, or a copper-tin-zinc-Invar alloy combination, its deformation temperature is between 90℃ and 150℃, which is beneficial for the timely pressure relief of the secondary battery 100.

[0092] The synergistic effect between the aforementioned 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, the first metal layer 411, due to its larger coefficient of thermal expansion, will expand relative to the second metal layer 412, causing the metal sheet 41 to bend and deform. This deformation will act on the sealing element 42. When the deformation reaches a certain level, the sealing element 42 will open, and the pressure inside the secondary battery 100 will be released in a timely manner.

[0093] The coefficient of thermal expansion (CTE) of various metal layers can be adjusted by modifying their composition. For example, in nickel-iron alloys, changing the ratio of nickel to iron affects the CTE; increasing the nickel content decreases the CTE. Invar alloys, adding small amounts of other elements such as carbon, silicon, and manganese increases the CTE. In nickel-chromium-iron alloys, adjusting the content of nickel, chromium, iron, and other alloying elements alters the CTE. In manganese-copper-nickel alloys, changing the ratio of the three main elements—manganese, copper, and nickel—adjusts the CTE. The CTE of nickel-chromium-iron alloys, copper-tin-zinc alloys, copper-zinc alloys, and alloy steels can all be adjusted by modifying the proportions of their components. For copper and nickel, small amounts of other elements, such as molybdenum or tungsten, can also be added. In other embodiments, the CTE of various metal layers can be adjusted through heat treatment, the addition of trace elements, and optimization of processing techniques; for example, the CTE may differ under different heat treatment conditions.

[0094] In the embodiments of this application, the shape memory alloy metal sheet 41 includes, but is not limited to, a two-layer metal layer structure. In other embodiments, it may also include a three-layer, four-layer, or other multi-layer structure. For example, the layer with a larger coefficient of thermal expansion is considered the active layer, and the layer with a smaller coefficient of thermal expansion is considered the passive layer. When the temperature changes, the active layer can bend and deform towards the passive layer, thereby opening the seal 42.

[0095] Referring to Figure 5, in this embodiment of the application, the metal sheet 41 further includes a third metal layer 413, which is stacked between the first metal layer 411 and the second metal layer 412. The intermediate third metal layer 413 can act as a buffer, dispersing the stress generated by the first metal layer 411 and the second metal layer 412 during deformation. For example, frequent deformation of the first metal layer 411 and the second metal layer 412 may cause fatigue or damage to the metal sheet 41, while the presence of the third metal layer 413 can extend the service life of the metal sheet 41, enabling it to work more stably. Furthermore, the regulating effect of the intermediate third metal layer 413 on heat conduction helps optimize the response speed and accuracy of the pressure relief assembly 40. More uniform and timely heat conduction allows the metal sheet 41 to deform rapidly when the internal temperature of the secondary battery 100 reaches a set value, opening the pressure relief channel.

[0096] In some embodiments, the coefficient of thermal expansion of the third metal layer 413 is G3, where G2 < G3 < G1. This better alleviates the stress caused by the first metal layer 411 and the second metal layer 412, reducing the risk of deformation of the metal sheet 41. The third metal layer 413 can be made of at least one of pure nickel, pure copper, or zirconium copper. Pure nickel, pure copper, or zirconium copper have good toughness and thermal conductivity, which is beneficial for stress dispersion and timely heat transfer.

[0097] In some embodiments, referring to Figures 6 to 8, the pressure relief assembly 40 further includes a connecting piece 43, which is disposed on the first wall surface 121 and has a second through hole 433 communicating with the first through hole 123, allowing gas inside the housing 10 to be discharged through the first through hole 123 and the second through hole 433. The connecting piece 43 can be connected to the housing 10 by welding or bonding.

[0098] The seal 42 is bonded between the connecting piece 43 and the first metal layer 411, and the metal piece 41 covers the second through hole 433, allowing the metal piece 41, the seal 42, and the connecting piece 43 to form a single unit. During installation, the seal 42 can be bonded between the metal piece 41 and the connecting piece 43 first, and then the connecting piece 43 can be connected to the housing 10, simplifying the installation process and improving installation accuracy. During disassembly, the entire pressure relief assembly 40 can be detached from the housing 10 by separating the connecting piece 43, ensuring high integrity of the pressure relief assembly 40 and facilitating its reuse.

[0099] The inventors of this application have discovered that the connecting piece 43 can also be made of a bimetallic shape memory alloy. Referring to Figures 9 and 10, along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the connecting piece 43 includes a fourth metal layer 431 and a fifth metal layer 432 stacked together. The second through hole 433 penetrates 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 sealing member 42 and the fifth metal layer 432. The coefficient of thermal expansion of the fourth metal layer 431 is G4, and the coefficient of thermal expansion of the fifth metal layer 432 is G5, where G4 > G5.

[0100] In the embodiments of this application, because the fourth metal layer 431 has a larger coefficient of thermal expansion, when the secondary battery 100 experiences an abnormal situation leading to a temperature rise, the fourth metal layer 431 expands more. Due to the constraint of the first wall portion 12, the central portion of the fourth metal layer 431 protrudes away from the first wall portion 12, causing the fourth metal layer 431 to partially detach from the seal 42. This weakens the adhesion between the connecting piece 43 and the seal 42, making it easier for the seal 42 to be opened, thereby achieving timely release of internal pressure in the secondary battery 100 and playing a pressure relief role. Furthermore, the bending direction of the connecting piece 43 is opposite to that of the metal piece 41, which further reduces the bonding area between the seal 42, the metal piece 41, and the connecting piece 43, further weakening the adhesion. This improves the sensitivity of the pressure relief component 40, enabling it to respond promptly to abnormal temperature changes in the secondary battery 100.

[0101] Similar to the aforementioned metal sheet 41, the fourth metal layer 431 is made of at least one of the following materials: nickel-chromium-iron alloy, nickel, copper, copper-tin-zinc alloy, copper-zinc alloy, or alloy steel. The fifth metal layer 432 is made of at least one of the following materials: nickel-iron alloy, Invar alloy, nickel-chromium-iron alloy, or manganese-copper-nickel alloy. The synergistic effect between the various metal materials effectively achieves the pressure relief function of the secondary battery 100.

[0102] In some embodiments, referring to Figure 11, only the connecting piece 43 may adopt a bimetallic shape memory alloy structure. When the secondary battery 100 experiences an abnormal situation that causes the temperature to rise, the central part of the fourth metal layer 431 can also protrude in the direction away from the first wall 12, thereby weakening the adhesion between the connecting piece 43 and the seal 42, which is conducive to the seal 42 being opened, thereby realizing the timely release of the internal pressure of the secondary battery 100.

[0103] Referring to Figures 12 to 14, observing along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the connecting piece 43 includes a first portion 43a overlapping 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 surrounds the second region 43a2, and the second region 43a2 surrounds the first through hole 123. For example, the first region 43a1 is fixed to the first wall portion 12 by welding, while the second region 43a2 does not require any operation and is directly attached to the first wall portion 12, or a predetermined gap space is provided between the second region 43a2 and the first wall portion 12.

[0104] In the embodiments of this application, the connecting piece 43 is fixed to the housing 10 only in the first region 43a1 near the edge, while its central part (including the second region 43a2) is relatively free. This structural design provides a certain degree of flexibility to the pressure relief assembly 40. When the internal pressure of the secondary battery 100 changes, since the central part of the connecting piece 43 is not fixed, it can better adapt to the outward bulging deformation of the center of the connecting piece 43, which is beneficial for timely pressure relief when the air pressure rises or the temperature changes.

[0105] In some implementations, viewed along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the connecting piece 43 also includes a second part 43b connected to the first part 43a, the second part 43b covering part of the first through hole 123. When the pressure inside the housing 10 increases, the gas can impact part of the second part 43b of the connecting piece 43, which is more conducive to the second part 43b driving the second region 43a2 to bulge in a direction away from the housing 10, thereby causing the connecting piece 43 to partially separate from the seal 42. This facilitates timely response to pressure changes inside the housing 10 and further reduces the risk of the secondary battery 100 exploding.

[0106] In some embodiments, referring to Figure 14, the width of the first region 43a1 is W1, and the width of the second region 43a2 is W2. If the width of the second region 43a2 is too small, it may be difficult for the second region 43a2 to protrude in the direction away from the housing 10 in a timely manner, thus making it difficult to release pressure in a timely manner. If the width of the second region 43a2 is too large, it may be possible for the connection strength between the connecting piece 43 and the housing 10 to be insufficient, affecting the sealing performance of the secondary battery 100. In the embodiments of this application, it is limited that 0.1mm≤W1≤1mm, and 1 / 10≤W1 / W2≤1 / 3, for example, 0.3mm≤W1≤3mm, which can make the secondary battery 100 have better sealing performance under normal operating conditions, and facilitate the second region 43a2 to protrude in the direction away from the first wall 12 under abnormal operating conditions, which is more conducive to opening the seal 42 and facilitating the timely pressure release of the secondary battery 100. The width of the first region 43a1 can be the difference between the outer diameter of the fitting circle containing the first region 43a1 and the inner diameter of the fitting circle containing the first region 43a1. The second region 43a2 is similar.

[0107] In some embodiments, when viewed along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the connecting piece 43 is annular. The annular shape is centrally symmetrical, ensuring that the force is evenly distributed around the circumference regardless of the direction of pressure application. When subjected to pressure from the internal pressure of the secondary battery 100 and the force transmitted by the deformation of the metal sheet 41, the annular connecting piece 43 experiences relatively uniform force. For example, when the internal pressure of the secondary battery 100 increases and the gas exerts an outward pushing force on the connecting piece 43, the force at each point on the edge of the annular connecting piece 43 is essentially the same. This reduces local stress concentration, allowing the connecting piece 43 to withstand pressure more stably and preventing damage due to excessive local stress.

[0108] Furthermore, the first through hole 123 is usually circular, and the annular connecting piece 43 can fit well with it, so that the annular connecting piece 43 can naturally cover the area around the first through hole 123. While improving the connection strength, it is easier to control the degree of coverage of the first through hole 123 through reasonable design (for example, the first part 43a and the second part 43b are set as described above) to ensure the timely response of the pressure relief function.

[0109] Regarding the outer diameter of the connecting piece 43, if the outer diameter is too large, it will occupy more space in the secondary battery 100, affecting the thickness of the secondary battery 100 and potentially causing a loss in the energy density of the secondary battery 100. If the outer diameter is too small, its connection area with the housing 10 will be small, resulting in insufficient support for the seal 42. When the internal pressure of the secondary battery 100 changes, the tensile and shear forces on the connecting piece 43 may cause the connection point to loosen or fall off, thereby affecting the normal operation of the pressure relief assembly 40.

[0110] In the embodiments of this application, please refer to Figure 15. The outer diameter of the connecting piece 43 is R, where 1mm≤R≤6mm. This can reduce the impact on the energy density of the secondary battery 100 and ensure that the connecting piece 43 and the sealing member 42 have sufficient connection area, thereby reducing the loosening or falling off of the connecting piece 43 and improving the reliability of the pressure relief assembly 40.

[0111] Preferably, 2mm≤R≤5mm can reduce the impact on the energy density of the secondary battery 100, while further reducing the risk of the connecting piece 43 becoming loose or falling off, and improving the reliability of the pressure relief assembly 40.

[0112] If the diameter of the first through-hole 123 is too large, it increases the difficulty of sealing, raising the risk of electrolyte leakage inside the secondary battery 100. It may also allow external air and moisture to enter the secondary battery 100, affecting the chemical properties of the electrolyte and potentially causing internal short circuits or other malfunctions. If the diameter of the first through-hole 123 is too small, the pressure relief efficiency decreases. In the event of a rapid increase in internal pressure (such as thermal runaway or short circuits), gas cannot be released in time, potentially causing the casing 10 to rupture or even explode, severely compromising the safety of the secondary battery 100.

[0113] In the embodiments of this application, the diameter of the first through hole 123 is R1, 0.5≤R1≤5.5mm, which can not only reduce the entry of external air, moisture and other substances into the secondary battery 100, but also facilitate the timely discharge of gas.

[0114] Regarding the diameter of the second through-hole 433, if the diameter is too large, external air and moisture will more easily enter the secondary battery 100 through it, increasing the risk of electrolyte leakage and internal short circuits. If the diameter is too small, it will restrict the gas discharge rate, leading to reduced pressure relief efficiency and making it prone to blockage. Impurities generated inside the secondary battery 100 (such as tiny particles of electrode material and solid substances produced by electrolyte decomposition) may accumulate at the second through-hole 433. Once blocked, gas cannot be discharged through this channel, causing the pressure relief function to fail and thus affecting the safety of the secondary battery 100.

[0115] In the embodiments of this application, the diameter of the second through hole 433 is R2, 0.1mm≤R2≤4mm, which can not only reduce the entry of external air, moisture and other substances into the secondary battery 100, but also reduce the risk of the second through hole 433 being blocked, and facilitate the timely discharge of gas.

[0116] Observing along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the area of ​​the first through hole 123 is S1, and the area of ​​the second through hole 433 is S2, where S2 < S1. The area of ​​the second through hole 433 is smaller than that of the first through hole 123, which can regulate the pressure relief rate to a certain extent 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 this gas are carried out 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 conditions, which helps to maintain the internal pressure of the secondary battery 100 within the normal range, thereby improving the performance stability of the secondary battery 100.

[0117] Furthermore, the area of ​​the second through-hole 433 is smaller than that of the pressure relief hole, which reduces the entry of external air and moisture into the secondary battery 100. During pressure relief, the connecting piece 43 restricts the contact between external substances and the electrolyte and electrode materials inside the secondary battery 100, allowing the chemical reaction inside the secondary battery 100 to proceed in a relatively stable environment. Specifically, the area of ​​the second through-hole 433 can be selected as 0.00785 mm². 2 ≤S2≤16mm 2 .

[0118] In some embodiments, referring to Figures 16 and 17, the pressure relief assembly 40 further includes a protective layer 44, which is disposed on the surface of the second metal layer 412 facing away from the first metal layer 411. This can reduce the impact, friction, etc., that the metal sheet 41 may be subjected to during the production, transportation, or use of the secondary battery 100. The protective layer 44 can act as a buffer layer, absorbing and dispersing these external forces, reducing scratches, deformation, or damage to the metal sheet 41, and improving the stability of the shape and performance of the metal sheet 41.

[0119] Regarding the material of the protective layer 44, in the embodiments of this application, the material of the protective layer 44 includes at least one selected from polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate, or polyetheretherketone. All of the above materials possess a certain strength and toughness, capable of withstanding certain external forces, and provide good protection for the metal sheet 41. Furthermore, they all exhibit good chemical stability, resisting chemical corrosion to a certain extent, which helps extend the service life of the metal sheet 41.

[0120] Regarding the thickness of the protective layer 44, if the protective layer 44 is too thick, the metal sheet 41 may not be able to deform in time, affecting the pressure relief function; if the thickness is too thin, it will not be able to provide effective protection for the metal sheet 41. In the embodiments of this application, along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the thickness of the protective layer 44 is D2, 0.01mm≤D2≤0.25mm. This can provide effective protection for the metal sheet 41 and facilitate the timely deformation of the metal sheet 41 when the temperature changes. Preferably, 0.01mm≤D2≤0.15mm.

[0121] Due to the support of the aforementioned protective layer 44, the overall strength of the metal sheet 41 is improved, the risk of deformation under normal operating conditions is reduced, and the pressure relief assembly 40 has better sealing performance under normal operating conditions. Therefore, in the embodiments of this application, the metal sheet 41 can be appropriately thinned. For example, along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the thickness of the metal sheet 41 is D1, where 0.01mm ≤ D1 ≤ 0.25mm.

[0122] The thinner metal sheet 41 has a shorter heat conduction path, and when the internal temperature of the secondary battery 100 changes, heat can be transferred more quickly within the metal sheet 41, enabling the bimetallic shape memory alloy metal sheet 41 to sense temperature changes and respond more rapidly.

[0123] Furthermore, the thinner metal sheet 41 has lower rigidity, so it is less affected by internal stress and other factors during deformation. This makes it easier to control the deformation of the metal sheet 41 when the temperature changes, and allows for more precise control of the opening and closing of the pressure relief component 40, thereby improving the accuracy and reliability of the pressure relief process of the secondary battery 100.

[0124] In the embodiments of this application, the melting point of the sealing element 42 is T, where 90℃≤T≤150℃.

[0125] Within the normal operating temperature range of the secondary battery 100 (generally -20℃ to 85℃), the seal 42 can remain solid and has good sealing performance. It can seal the installation gap between the metal sheet 41 and the housing 10, effectively prevent electrolyte leakage inside the secondary battery 100, and block external air and moisture from entering the secondary battery 100.

[0126] When the secondary battery 100 malfunctions, such as overcharging, short circuit, or localized overheating, its internal temperature rises sharply. When the temperature reaches the melting point of the seal 42 (90°C to 150°C), the seal 42 begins to melt, allowing the pressure relief assembly 40 to open promptly, reducing the risk of excessive internal pressure and explosion in the secondary battery 100. The deformation temperature of the metal sheet 41 can be set to 90°C to 150°C. For example, the metal sheet 41 can be made of copper-nickel-chromium-iron alloy, copper-zinc alloy-manganese-copper-nickel alloy, or copper-tin-zinc alloy-Invar alloy, all with deformation temperatures between 90°C and 150°C. These materials can work in conjunction with the seal 42 to facilitate timely pressure relief of the secondary battery 100.

[0127] Regarding the material of the seal 42, in the embodiments of this 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, and reduces damage to the seal 42 due to chemical corrosion, thereby improving the sealing performance of the seal 42. Furthermore, each material has low permeability to gases and liquids, which can reduce internal electrolyte leakage and prevent external air, moisture, etc., from entering the secondary battery 100, thus helping to maintain the normal operation of the secondary battery 100.

[0128] Regarding the adjustment of the melting point of the seal at 42:

[0129] Polypropylene's melting point can be adjusted through copolymerization modification: by copolymerizing with small amounts of other monomers, the melting point of polypropylene can be adjusted. For example, copolymerization with ethylene forms ethylene-propylene rubber (EPR) modified polypropylene. The introduction of ethylene monomers alters the molecular chain structure of polypropylene, reducing the regularity of the molecular chains and decreasing crystallinity, thereby lowering the melting point. The melting point of this modified polypropylene can be adjusted according to the ethylene content; generally, as the ethylene content increases, the melting point gradually decreases.

[0130] The melting point of polyethylene can be adjusted by density regulation: for example, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE) have different melting points.

[0131] The melting point of polyvinylidene fluoride (PVDF) can be adjusted by controlling its crystallinity. This is achieved by altering processing conditions, such as stretching and annealing, which in turn affect the melting point. For example, annealing at an appropriate temperature can improve the crystallinity of PVDF, leading to higher melting points. Conversely, rapid cooling may decrease crystallinity, resulting in lower melting points. PVDF can also be modified through copolymerization.

[0132] The melting point of polytetrafluoroethylene (PTFE) can be adjusted by adding fillers: for example, adding inorganic fillers such as glass fiber and carbon fiber can change the thermal properties of the material, such as improving thermal conductivity and making the temperature distribution more uniform during heating. This may result in different thermal behaviors in practical applications, indirectly affecting its processing and performance.

[0133] If the thickness of seal 42 is too large, it may increase the resistance to opening the pressure relief channel, potentially causing a delay in the pressure relief action. If the thickness is too small, it may not provide sufficient sealing force, potentially leading to electrolyte leakage or the entry of outside air and moisture into the battery.

[0134] In the embodiments of this application, referring to FIG17, along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the thickness of the sealing element 42 is D3, 0.01mm≤D3≤0.5mm. This can improve the sealing performance under normal operating conditions of the secondary battery 100, and can promptly open the pressure relief channel under abnormal conditions of the secondary battery 100 (pressure increase or temperature increase).

[0135] Secondly, this application also proposes an electronic device, including a secondary battery 100 as described in any of the embodiments of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0136] Example 1-1

[0137] Preparation of the positive electrode sheet:

[0138] The positive electrode active material is lithium iron phosphate, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and stirred evenly under vacuum. An aluminum foil with a thickness of 8 μm and a length of 1000 mm was selected as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material.

[0139] Preparation of negative electrode sheet:

[0140] A negative electrode active material (graphite powder), silicon powder, conductive carbon black (Super P), and binder (styrene-acrylic rubber (SD-3)) were mixed in a weight ratio of 89.5:8:1:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred evenly. A copper foil with a thickness of 5 μm and a length of 1050 mm was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated onto one surface of the copper foil and dried at 90°C to obtain a single-sided negative electrode sheet. After completing the above steps, the single-sided coating of the negative electrode sheet was finished. The above steps were then repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. A second groove was created in one of the negative electrode active material layers using a laser cleaning process. A portion of the negative electrode tab was then welded to the negative electrode current collector within the second groove.

[0141] Preparation of the separating membrane:

[0142] A porous separator membrane was prepared by using polyethylene as a 7μm substrate layer and polyvinylidene fluoride as an adhesive layer, with an alumina ceramic layer of 2μm thickness placed on the side of the adhesive layer away from the substrate layer.

[0143] Electrolyte preparation:

[0144] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0145] Preparation of metal sheets:

[0146] Select thickness D 11 A 0.15mm copper-zinc alloy (brass) is used as the first metal layer, with a thickness D. 12 A nickel-iron alloy with a thickness of 0.15 mm is used 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 D1 of 0.3 mm. The coefficient of thermal expansion of the copper-zinc alloy is G1 (18.5 × 10⁻⁶). -6 The coefficient of thermal expansion (°C) is greater than that of nickel-iron alloys, G2 (9.5 × 10⁻⁶). -6 / ℃).

[0147] Preparation of lithium-ion batteries:

[0148] The positive electrode sheet is welded to the aluminum positive electrode tab, and the negative electrode sheet is welded to the nickel negative electrode tab. The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and wound to obtain the electrode assembly. The electrode assembly is placed in a steel housing, with the positive electrode tab welded to the terminal post on the housing and the negative electrode tab welded to the housing. The housing has a first through-hole with a diameter R1 of 1 mm. After removing moisture at 80°C, electrolyte is injected. Polypropylene is used as a sealing element, and a metal sheet is bonded to the housing through the sealing element, covering the first through-hole. After encapsulation, formation, capacity testing, and voltage and internal resistance testing, a lithium-ion battery is obtained.

[0149] Unlike Example 1-1, the relevant parameters in Examples 1-2 to 1-37 and Comparative Examples 1-1 to 1-2 are shown in Table 1 below. In Comparative Example 1-1, a single layer of nickel-iron alloy was used as the metal sheet. In Comparative Example 1-2, two layers of nickel-iron alloy were used as the first metal layer and the second metal layer, respectively, i.e., G1=G2.

[0150] Standard operating condition test: Store at 80℃±5℃ for 48 hours. If the lithium-ion battery shows no leakage, the test is considered passed.

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

[0152] First, set the test environment temperature to 23℃±2℃ and allow the test sample to rest for 5 minutes. Next, charge the lithium-ion battery sample at a constant current (DC) of 0.2C to 3.0V. After completing the charging operation, allow the sample to rest for another 5 minutes to allow the lithium-ion battery to have a brief period of stabilization after charging.

[0153] The furnace temperature for testing was adjusted to 37℃ (±2℃), and the lithium-ion battery samples were allowed to stand in this high-temperature environment for 2 hours (Rest 2H) to allow the samples to fully adapt to the high-temperature environment so as to observe the performance of the samples under this high-temperature condition and in subsequent operations.

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

[0155] After completing the above series of complex charging operations, let the lithium-ion battery sample rest for another 5 minutes.

[0156] Test Procedure: ① Inspect the appearance and take photos before and after the test; ② Place the temperature sensing wire near the anode tab; ③ Place the lithium-ion battery sample horizontally in the chamber and heat it to 130±2°C at a rate of 5±2°C and hold for 30 minutes; ④ Measurement frequency: Use 1KHz for voltage and internal resistance measurement, after pretreatment and after testing; ⑤ Judgment criteria: No explosion, no smoke, no fire.

[0157] Each group consists of 20 lithium-ion batteries, which undergo routine testing and thermal shock testing. Failure in either process is considered a test failure. The number of test failures is N, and the test failure rate is N / 20.

[0158] Table 1

[0159]

[0160] According to Table 1 above, and in conjunction with Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-2, the failure rate in Examples 1-1 to 1-7 is significantly lower than that in Comparative Examples 1-1 to 1-2. In Examples 1-1 to 1-7, the difference in thermal expansion coefficients of the two metal layers is used to form a metal sheet of a bimetallic shape memory alloy. Because the thermal expansion coefficient of the first metal layer is greater, when the secondary battery experiences an abnormal situation that causes the temperature to rise, the first metal layer expands more, causing the edge of the first metal layer to bend and lift towards the second metal layer. This causes the first metal layer to partially detach from the seal, weakening the adhesion between the metal sheet and the seal, making it easier for the seal to be opened. This allows for the timely release of internal pressure in the secondary battery, thus playing a role in depressurization.

[0161] In Examples 1-1 to 1-7, Examples 1-8 to 1-12, Examples 1-13 to 1-17, Examples 1-23 to 1-27, and Examples 1-28 to 1-32, in D 11 / D 12 Under consistent conditions, the overall failure rate is lower than that of Examples 1-18 to 1-22 and Examples 1-33 to 1-37. In Examples 1-18 to 1-22, the overall thickness of the metal sheet is too large, requiring more heat absorption, which may make it difficult for the metal sheet to deform and bend in time, thus leading to difficulty in timely pressure relief. In Examples 1-33 to 1-37, the thickness of the metal sheet is too small, which may affect the sealing performance. For example, during the normal operating condition test of lithium-ion batteries, it may cause the pressure relief component to be blown open, resulting in test failure. Therefore, in the embodiments of this application, the thickness of the metal sheet can be selected as 0.04mm≤D1≤1mm.

[0162] In Examples 1-1 to 1-7, the failure rate of Examples 1-1 to 1-5 is lower than that of Examples 1-6 to 1-7. In Examples 1-6, the thickness of the first metal layer is relatively large, which may lead to excessive bending of the metal sheet, making it prone to bending even with slight heating, thus affecting the normal operation of the lithium-ion battery. In Examples 1-7, the thickness of the second metal layer is relatively large, which may make it difficult for the first metal layer to deform the second metal layer and to break through the seal, thus potentially making it difficult for the lithium-ion battery to release pressure in a timely manner. Similarly, the failure rate of Examples 1-8 to 1-10 is lower than that of Examples 1-11 to 1-12, the failure rate of Examples 1-13 to 1-15 is lower than that of Examples 1-16 to 1-17, the failure rate of Examples 1-23 to 1-25 is lower than that of Examples 1-26 to 1-27, and the failure rate of Examples 1-28 to 1-30 is lower than that of Examples 1-31 to 1-32. Therefore, 1≤D can be selected. 11 / D 12 ≤5.

[0163] Unlike Example 1-1, the first metal layer and the second metal layer in Examples 2-1 to 2-30 have different coefficients of thermal expansion, and the relevant parameters are shown in Table 2 below.

[0164] Table 2

[0165]

[0166] According to Table 2 above, the failure rates in Examples 2-2 to 2-5 are lower than those in Examples 2-1 and 2-6. In Example 2-1, the difference in thermal expansion coefficients between the first and second metal layers is relatively small, which may result in less deformation of the metal sheet, potentially insufficient to quickly and effectively open the pressure relief channel. In Example 2-6, the difference in thermal expansion coefficients between the first and second metal layers is relatively large, which may lead to excessive bending of the metal sheet, making it prone to rapid bending and potentially causing faster failure. In Examples 2-2 to 2-5, the difference in thermal expansion coefficients between the first and second metal layers is optimal, which is beneficial for the normal use of lithium-ion batteries under normal operating conditions and allows for timely response to temperature changes, facilitating timely pressure relief in abnormal situations. Similarly, in Examples 2-8 to 2-11, the test failure rate is lower than that in Examples 2-7 and 2-12; in Examples 2-14 to 2-17, the test failure rate is lower than that in Examples 2-13 and 2-18; in Examples 2-20 to 2-23, the test failure rate is lower than that in Examples 2-19 and 2-24; and in Examples 2-26 to 2-29, the test failure rate is lower than that in Examples 2-25 and 2-30. Therefore, in the embodiments of this application, 4×10 can be selected. -6 / ℃≤G1-G2≤15×10 -6 / ℃.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A secondary battery, comprising a casing, the casing enclosing a receiving cavity, the casing including a first wall portion, the first wall portion including a first wall surface facing away from the receiving cavity and a second wall surface facing the receiving cavity, the first wall portion having a first through hole penetrating the first wall surface and the second wall surface; characterized in that, The secondary battery also includes a pressure relief assembly, which 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 together, the sealant is bonded between the first metal layer and the first wall surface, and the metal sheet covers the first through hole; The coefficient of thermal expansion of the first metal layer is G1, and the coefficient of thermal expansion of the second metal layer is G2, where G1 > G2.

2. 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 metal sheet is D1, where 0.04mm≤D1≤1mm.

3. The secondary battery according to claim 2, characterized in that, The thickness of the first metal layer is D along the direction from the first wall surface to the second wall surface. 11 The thickness of the second metal layer is D 12 , 1≤D 11 / D 12 ≤5.

4. The secondary battery according to any one of claims 1 to 3, 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.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The metal sheet further includes a third metal layer, which is stacked between the first metal layer and the second metal layer.

6. The secondary battery according to claim 5, characterized in that, The third metal layer includes pure nickel, pure copper, or zirconium copper.

7. The secondary battery according to claim 5 or 6, characterized in that, The coefficient of thermal expansion of the third metal layer is G3, where G2 < G3 < G1.

8. The secondary battery according to any one of claims 1 to 6, characterized in that, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃。 9. The secondary battery according to any one of claims 1 to 8, characterized in that, The pressure relief assembly further includes a connecting piece disposed on the first wall surface. The connecting piece has a second through hole that communicates with the first through hole. The sealing element 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 piece includes a fourth metal layer and a fifth metal layer stacked together; The second through hole penetrates 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 G4, and the coefficient of thermal expansion of the fifth metal layer is G5, where G4 > G5.

11. The secondary battery according to claim 10, characterized in that, Viewed along the direction from the first wall to the second wall, the connecting piece includes a first portion that overlaps with the first wall portion, the first portion including a first area fixed to the first wall portion and a second area not fixed to the first wall portion; The first region surrounds the second region, and the second region surrounds the first through hole.

12. The secondary battery according to claim 11, characterized in that, Viewed along the direction from the first wall surface to the second wall surface, the connecting piece also includes a second part connected to the first part, the second part covering part of the first through hole.

13. The secondary battery according to claim 11, characterized in that, The width of the first region is W1, 0.1mm≤W1≤1mm, 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, Viewed along the direction from the first wall surface to the second wall surface, the connecting piece is annular, and the outer diameter of the connecting piece is R, where 1mm≤R≤6mm.

15. The secondary battery according to claim 14, characterized in that, 2mm≤R≤5mm.

16. The secondary battery according to any one of claims 9 to 13, characterized in that, The diameter of the first through hole is R1, where 0.5 ≤ R1 ≤ 5.5 mm; The diameter of the second through hole is R2, where 0.1mm ≤ R2 ≤ 4mm.

17. The secondary battery according to any one of claims 9 to 13, characterized in that, Viewed along the direction from the first wall surface to the second wall surface, the area of ​​the first through hole is S1, the area of ​​the second through hole is S2, S2 < S1, and 0.00785 mm. 2 ≤S2≤16mm 2 .

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The pressure relief assembly further includes a protective layer disposed on the surface of the second metal layer opposite to the first metal layer.

19. The secondary battery according to claim 18, characterized in that, Along the direction from the first wall surface to the second wall surface, the thickness of the metal sheet is D1, where 0.01mm≤D1≤0.25mm.

20. The secondary battery according to claim 19, characterized in that, Along the direction from the first wall surface to the second wall surface, the thickness of the protective layer is D2, 0.01mm≤D2≤0.25mm.

21. The secondary battery according to claim 20, characterized in that, 0.01mm≤D2≤0.15mm.

22. The secondary battery according to claim 18, characterized in that, The protective layer is made of at least one of polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate, or polyetheretherketone.

23. The secondary battery according to any one of claims 1 to 22, characterized in that, The melting point of the seal is T, where 90℃≤T≤150℃.

24. The secondary battery according to any one of claims 1 to 23, characterized in that, Along the direction from the first wall surface to the second wall surface, the thickness of the seal is D3, where 0.01mm≤D3≤0.5mm.

25. The secondary battery according to any one of claims 1 to 24, characterized in that, The material of the seal includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, or polytetrafluoroethylene.

26. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 25.

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