Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment. The secondary battery comprises a shell, and an accommodating cavity is enclosed by the shell. The shell comprises a first wall part, the first wall part comprises a first wall face deviating from the containing cavity and a second wall face facing the containing cavity, and the first wall part is provided with a first through hole penetrating through the first wall face and the second wall face. The secondary battery further comprises a pressure relief assembly, and the pressure relief assembly comprises a metal sheet and a sealing piece. In the direction from the second wall surface to the first wall surface, the metal sheet comprises a first metal layer and a second metal layer which are stacked, 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 thermal expansion coefficient of the first metal layer is G1, the thermal expansion coefficient of the second metal layer is G2, and G1 is larger than G2. The internal temperature change of the secondary battery can be responded in time, the pressure of the secondary battery can be released in time, and the risk of explosion of the secondary battery is reduced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular 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 mobile phones, laptops, electric vehicles and other fields, and the quality and safety requirements for batteries are becoming increasingly higher. However, when the battery is in a high temperature environment or a short circuit occurs, it is easy to cause thermal runaway of the battery, and the internal gas pressure of the battery gradually increases, which can easily cause the battery to catch fire or even explode, posing a safety risk. Summary of the invention

[0003] One purpose of the embodiments of the present application is to provide a secondary battery and an electronic device to reduce the technical problem that the secondary battery is prone to explosion.

[0004] In the first aspect, an embodiment of the present application proposes a secondary battery, including a shell, wherein the shell encloses a accommodating cavity. The shell includes a first wall portion, the first wall portion includes a first wall surface facing away from the accommodating cavity and a second wall surface facing the accommodating cavity, and the first wall portion is provided with a first through hole penetrating the first wall surface and the second wall surface. The secondary battery also includes a pressure relief assembly, and the pressure relief assembly 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, the seal is bonded between the first metal layer and the first wall surface, and the metal sheet covers the first through hole. The thermal expansion coefficient of the first metal layer is G1, and the thermal expansion coefficient of the second metal layer is G2, and G1>G2.

[0005] In the above technical solution, the difference in thermal expansion coefficients of the two metal layers is used to form a metal sheet of a bimetallic memory alloy. Since the thermal expansion coefficient 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 tilt toward the second metal layer, thereby partially separating the first metal layer from the seal. The bonding force between the metal sheet and the seal is weakened, which is more conducive to the seal being opened, thereby achieving timely release of the internal pressure of the secondary battery and playing a role in pressure relief.

[0006] 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 in a timely manner, which helps to release the gas in a timely manner, reduce the sharp rise in the internal pressure of the secondary battery, and effectively reduce the risk of explosion of the secondary battery. In addition, the shape memory property of the bimetallic memory alloy enables the metal sheet to return to its original state after the temperature drops, and to a certain extent, it can cooperate with the seal again to restore the sealing state of the secondary battery, which is conducive to the reuse of the pressure relief component.

[0007] In some embodiments, along the direction from the first wall to the second wall, the thickness of the metal sheet is D1, 0.04mm≤D1≤1mm. This is beneficial to the normal use of the secondary battery under normal working conditions, 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 under abnormal conditions.

[0008] In some embodiments, the thickness of the first metal layer along the direction from the first wall to the second wall is D 11 , 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. At the same time, it can respond to the temperature change of the secondary battery in time, which is beneficial to the timely pressure relief of the secondary battery under abnormal conditions.

[0009] 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. The metal sheet can work normally within a normal 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 a copper-nickel-chromium-iron combination, a copper-zinc alloy-manganese-copper-nickel combination, a copper-tin-zinc-Invar alloy combination, etc., and its deformation temperature is between 90°C and 150°C, which is conducive to timely pressure relief of the secondary battery.

[0010] In some embodiments, the metal sheet also includes a third metal layer, and the third metal layer is stacked between the first metal layer and the second metal layer. The metal sheet needs to be heat treated during the battery manufacturing process. During the heat treatment, the two metal layers are prone to deformation due to different thermal expansion coefficients. The third metal layer can play a buffering role and reduce the deformation and separation of each metal layer caused by excessive local stress. In addition, the regulating effect of the third metal layer on heat conduction helps to optimize the response speed and accuracy of the pressure relief component. More uniform and timely heat conduction can make the metal sheet deform rapidly when the internal temperature of the secondary battery reaches the set value, opening the pressure relief channel. Among them, the third metal layer includes pure nickel, pure copper or zirconium copper. Pure nickel, pure copper or zirconium copper have good toughness and thermal conductivity, which is conducive to the dispersion of stress and the timely transfer of heat.

[0011] In some embodiments, the thermal expansion coefficient of the third metal layer is G3, G2<G3<G1, which can better relieve the stress caused by the first metal layer and the second metal layer and reduce the risk of deformation of the metal sheet.

[0012] In some embodiments, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃. It is beneficial to the normal use of the secondary battery, and can respond to the temperature change of the secondary battery in time, which is beneficial to the timely pressure relief of the secondary battery under abnormal conditions.

[0013] In some embodiments, the pressure relief assembly further includes a connecting sheet disposed on the first wall, the connecting sheet is provided with a second through hole, the second through hole is communicated with the first through hole, a sealing member is bonded between the connecting sheet 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 sheet, and then the connecting sheet can be connected to the housing, which can simplify the installation process and help improve the installation accuracy. During disassembly, the entire pressure relief assembly can be removed from the housing by separating the connecting sheet and the housing, which can make the pressure relief assembly have a higher integrity and is conducive to the reuse of the pressure relief assembly.

[0014] In some embodiments, 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 stacked. 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 arranged between the seal 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.

[0015] Since the thermal expansion coefficient of the fourth metal layer is larger, when the temperature rises due to an abnormal situation in the secondary battery, the fourth metal layer expands more. Due to the restriction of the first wall, the central portion of the fourth metal layer will bulge away from the first wall, thereby partially separating the fourth metal layer from the seal. The bonding force between the connecting sheet and the seal is weakened, which is more conducive to the seal being opened, thereby achieving timely release of the internal pressure of the secondary battery and playing a role in pressure relief. In addition, the bending direction of the connecting sheet is opposite to that of the metal sheet, which can further reduce the bonding area between the seal and the metal sheet and the connecting sheet, and further weaken the bonding force, which is conducive to improving the sensitivity of the pressure relief component, thereby being able to respond to abnormal temperature changes of the secondary battery in a timely manner.

[0016] In some embodiments, 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 arranged around the second area, and the second area is arranged around the first through hole. The connecting piece is only fixed to the shell in the first area close to the edge, and its central part is relatively free. This structural design provides a certain 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 fixed, it can better conform to the bulging deformation of the center of the connecting piece, which is conducive to timely pressure relief when the air pressure increases or the temperature changes.

[0017] In some embodiments, when viewed 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. When the pressure inside the shell increases, the gas may impact 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 shell, thereby partially separating the connecting piece from the sealing member.

[0018] In some embodiments, the width of the first area is W1, 0.1mm≤W1≤1mm, and the width of the second area is W2, 1 / 10≤W1 / W2≤1 / 3. This can enable the secondary battery to have better sealing performance under normal operating conditions, and help the secondary battery to protrude the second area away from the first wall under abnormal operating conditions, which is more conducive to opening the seal and facilitating timely pressure relief of the secondary battery.

[0019] In some embodiments, the connecting piece is annular when viewed from the first wall to the second wall, and the outer diameter of the connecting piece is R, 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 a sufficient connection area, reduce the loosening or falling of the connecting piece, and improve the reliability of the pressure relief assembly. Preferably, in some embodiments, 2mm≤R≤5mm.

[0020] In some embodiments, the diameter of the first through hole is R1, 0.5≤R1≤5.5mm, which can not only reduce the entry of external air, moisture, etc. into the secondary battery, but also facilitate the timely discharge of gas. The diameter of the second through hole is R2, 0.1mm≤R2≤4mm, which can not only reduce the entry of external air, moisture, etc. into the secondary battery, but also reduce the risk of the second through hole being blocked, which is more conducive to the timely discharge of gas.

[0021] In some embodiments, when viewed from the first wall to the second wall, the area of ​​the first through hole is S1, the area of ​​the second through hole is S2, S2<S1, 0.00785mm 2 ≤S2≤16mm 2 The connecting piece can limit the contact between external substances and the electrolyte and electrode materials inside the secondary battery, so that the chemical reaction inside the secondary battery can be carried out in a relatively stable environment.

[0022] In some embodiments, the pressure relief assembly further includes a protective layer, which is disposed on the surface of the second metal layer away from the first metal layer. The protective layer can act as a buffer layer to absorb and disperse these external forces, reduce scratches, deformation or damage to the metal sheet, and improve the stability of the shape and performance of the metal sheet.

[0023] In some embodiments, along the direction from the first wall to the second wall, the thickness of the metal sheet is D1, 0.01mm≤D1≤0.25mm. The thinner the metal sheet, the shorter the heat conduction path. When the temperature inside the secondary battery changes, the heat can be transferred faster in the metal sheet, so that the metal sheet of the bimetallic layer memory alloy can sense the temperature change more quickly and respond.

[0024] In some embodiments, along the direction from the first wall to the second wall, the thickness of the protective layer is D2, 0.01mm≤D2≤0.25mm. This can effectively protect the metal sheet and facilitate the timely deformation of the metal sheet when the temperature changes. Preferably, 0.01mm≤D2≤0.15mm.

[0025] In some embodiments, the material of the protective layer includes at least one of polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate or polyetheretherketone. Each material has certain strength and toughness, can withstand certain external forces, and has a better protective effect on the metal sheet.

[0026] 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 a good sealing performance and can seal the installation gap between the metal sheet and the shell. 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 in time, reducing the internal pressure of the secondary battery from being too high and causing an explosion.

[0027] In some embodiments, the thickness of the sealant along the direction from the first wall to the second wall is D3, 0.01mm≤D3≤0.5mm. The sealing performance can be improved when the secondary battery is working normally, and the pressure relief channel can be opened in time when the secondary battery is abnormal.

[0028] In some embodiments, the material of the sealing element includes at least one of polypropylene, polyethylene, polyvinylidene fluoride or polytetrafluoroethylene.

[0029] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0030] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0032] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0033] Figure 2 An exploded schematic diagram of a secondary battery according to some embodiments of the present application;

[0034] Figure 3 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0035] Figure 4 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application (pressure relief state);

[0036] Figure 5 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0037] Figure 6 An exploded schematic diagram of a secondary battery according to some embodiments of the present application;

[0038] Figure 7 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0039] Figure 8 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application (pressure relief state);

[0040] Fig. 9 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0041] Fig.10 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application (pressure relief state);

[0042] Fig.11 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application (pressure relief state);

[0043] Fig.12 A front view of a secondary battery according to some embodiments of the present application (viewed in a direction perpendicular to the first wall);

[0044] Fig.13 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0045] Fig.14 This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application (pressure relief state);

[0046] Fig.15 A partial structural schematic diagram of a secondary battery in some embodiments of the present application;

[0047] Fig.16This is a schematic diagram of the structure of the pressure relief assembly of some embodiments of the present application;

[0048] Fig.17 Schematic diagram of the stacked structure of metal sheets and protective layers in some embodiments of the present application.

[0049] Description of reference numerals:

[0050] 100. Secondary battery;

[0051] 10. Shell; 10a. Main body; 10b. Cover; 11. Accommodating cavity; 12. First wall; 121. First wall surface; 122. Second wall surface; 123. First through hole;

[0052] 20. Electrode assembly;

[0053] 30. Pole;

[0054] 40. Pressure relief assembly;

[0055] 41. metal sheet; 411. first metal layer; 412. second metal layer; 413. third metal layer;

[0056] 42. sealing member; 421. third through hole;

[0057] 43, connecting piece; 43a, first part; 43a1, first area; 43a2, second area; 43b, second part; 431, fourth metal layer; 432, fifth metal layer; 433, second through hole;

[0058] 44. Protective layer;

[0059] X, first direction; Y, second direction. DETAILED DESCRIPTION

[0060] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0061] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0062] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0063] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0064] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0065] In the first aspect, the present application proposes 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 pole 30, and a pressure relief assembly 40. The electrode assembly 20 is disposed in the housing 10, one end of the pole 30 is connected to the electrode assembly 20, and the other end is exposed from the housing 10, and the pole 30 is used to lead out one polarity of the secondary battery 100. The pressure relief assembly 40 is disposed in the housing 10, and when the air pressure in the housing 10 is high, the pressure relief assembly 40 can discharge part of the gas in the housing 10.

[0066] For the housing 10, please refer 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 infiltrates the electrode assembly 20 in the receiving cavity 11, thereby generating an electrochemical reaction. In the embodiment of the present application, the housing 10 can be formed by punching a conductive metal layer, and the thickness of the conductive metal layer can be set to 0.1 mm to 0.4 mm, so that the housing 10 has a high punching strength.

[0067] The conductive metal layer may be made of aluminum, steel, stainless steel, nickel, copper or magnesium alloy, so that the shell 10 can lead to a certain polarity of the secondary battery 100 and the pole 30 can lead to another polarity.

[0068] The housing 10 may be in a square, trapezoidal or cylindrical shape, etc., and a square housing 10 is taken as an example. Figure 1 and Figure 2The housing 10 includes a main body 10a and a cover 10b. The main body 10a is provided with a pit, and one end of the main body 10a is open, and the electrode assembly 20 can be directly placed in the pit through the open end. The cover 10b is connected to the main body 10a and covers the pit, so that the pit forms a receiving chamber 11.

[0069] Please refer to further Figure 3 The shell 10 includes a first wall portion 12, and the first wall portion 12 includes a first wall surface 121 facing away from the accommodating chamber 11 and a second wall surface 122 facing the accommodating chamber 11. The first wall portion 12 is provided with a first through hole 123, and the first through hole 123 passes through the first wall surface 121 and the second wall surface 122, and the first through hole 123 is communicated with the accommodating chamber 11. When the air pressure in the shell 10 increases, part of the gas can be discharged to the outside through the first through hole 123, which can reduce the explosion risk of the secondary battery 100. The first through hole 123 can also be used as a liquid injection hole. During the assembly process of the secondary battery 100, when the cover body 10b is connected and sealed with the main body 10a, the electrolyte can be directly injected into the accommodating chamber 11 through the first through hole 123 to facilitate the preparation of the secondary battery 100.

[0070] Regarding the electrode assembly 20 , the electrode assembly 20 is disposed in the accommodating cavity 11 of the shell 10 , and the shape of the electrode assembly 20 can be configured to match the shell 10 to fully utilize the space of the accommodating cavity 11 of the shell 10 and improve the energy density of the secondary battery 100 .

[0071] The electrode assembly 20 includes a positive electrode sheet (not shown in the figure), a negative electrode sheet (not shown in the figure) and a separator (not shown in the figure), and the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form a wound electrode assembly 20. Alternatively, a plurality of positive electrode sheets and a plurality of negative electrode sheets are alternately stacked, and a separator is provided between adjacent positive electrode sheets and negative electrode sheets to form a stacked electrode assembly 20.

[0072] The negative electrode sheet of the electrode assembly 20 can be directly electrically connected to the shell 10, so that the shell 10 leads to the negative electrode, and the positive electrode sheet of the electrode assembly 20 can be electrically connected to the pole 30, so that the pole 30 leads to the positive electrode. In some other embodiments, the shell 10 can also lead to the positive electrode, and the pole 30 leads to the negative electrode.

[0073] For the above-mentioned pole 30, please refer to Figure 1 and Figure 2The pole 30 is disposed on the first wall portion 12, a portion of the pole 30 is electrically connected to the electrode assembly 20 in the accommodating cavity 11, and the other portion is exposed from the first wall portion 12. In the embodiment of the present application, the pole 30 and the shell 10 have opposite polarities, and an insulating member (not shown in the figure) can be disposed between the pole 30 and the shell 10 to reduce the occurrence of short circuits, and the insulating member can be bonded between the pole 30 and the first wall portion 12, which can connect the pole 30 and the shell 10 on the one hand, and seal the installation gap between the pole 30 and the shell 10 on the other hand, thereby improving the sealing performance of the secondary battery 100.

[0074] 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 . 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 .

[0075] When the secondary battery 100 is in a high temperature environment or short-circuited, the secondary battery 100 is prone to thermal runaway, and the air pressure inside the housing 10 gradually increases and impacts the metal sheet 41 and the seal 42, so that the seal 42 is opened, thereby forming a pressure relief channel connecting the accommodating chamber 11 with the outside, which can reduce the explosion of the secondary battery 100. The seal 42 can also be provided with a third through hole 421, which is connected to the first through hole 123, so as to facilitate the pressure relief of the seal 42 when it is opened.

[0076] 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.

[0077] 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. The thermal expansion coefficient of the first metal layer 411 is G1, the thermal expansion coefficient of the second metal layer 412 is G2, and G1>G2.

[0078] In the embodiment of the present application, 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, cooperates with the seal 42 and jointly maintains 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.

[0079] 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.

[0080] 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.

[0081] In addition, the shape memory property of the bimetallic layer memory alloy enables the metal sheet 41 to return to its original state after the temperature drops. 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 state and, to a certain extent, can cooperate with the seal 42 again to restore the sealing state of the secondary battery 100, which is beneficial to the reuse of the pressure relief assembly 40.

[0082] The pole 30 and the pressure relief assembly 40 can both be disposed on the first wall portion 12 , and there is a large space between the pole 30 and the electrode assembly 20 , which is beneficial to the exhaust and pressure relief of the pressure relief assembly 40 .

[0083] For the measurement of the thermal expansion coefficient of the metal layer, a dilatometer can be used. First, prepare a rectangular sample to ensure that the surface of the sample is smooth and free of defects. Using a dilatometer, calibrate the equipment to ensure the accuracy of the measurement. Place the sample in the dilatometer and test it in a controlled temperature environment. Change the temperature slowly and evenly to measure the dimensional change of the sample. During the temperature change, the dilatometer will record the length change of the sample and record the length change data at different temperatures. Use the formula to calculate the linear thermal expansion coefficient G = ΔL / (L0×ΔT), where ΔL is the length change, L0 is the initial length, and ΔT is the temperature change.

[0084] In the embodiments of this application, please refer to Figure 3 , along the direction from the first wall 121 to the second wall 122 (first direction X), the thickness of the metal sheet 41 is D1, 0.04mm≤D1≤1mm. This is conducive to the normal use of the secondary battery 100 under normal working conditions, so that the secondary battery 100 has better sealing performance; and it can respond to the temperature change of the secondary battery 100 in time, reduce the opening or closing of the pressure relief component 40 at an inappropriate temperature, and is conducive to the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0085] As for the thickness ratio of the first metal layer 411 to the second metal layer 412, if the thickness ratio is too large, the first metal layer 411 with a larger thermal expansion coefficient will be thicker, which may cause the metal sheet 41 to bend excessively, and easily cause stress concentration. During the deformation process caused by temperature changes, a large stress may be generated at the interface between the first metal layer 411 and the second metal layer 412, which may cause the metal sheet 41 to be damaged by cracks or delamination, affecting the service life of the pressure relief component 40 and being unfavorable for the reuse of the pressure relief component 40; and, if the thickness ratio is too large, the metal sheet 41 may bend when slightly heated, which may affect the normal operation of the secondary battery. If the thickness ratio is too small, that is, the thickness of the first metal layer 411 is small, 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, resulting in an increased risk of explosion.

[0086] 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 , the thickness of the second metal layer 412 is D 12 , 1≤D 11 / D 12≤5. The excessive bending of the metal sheet 41 can be reduced, which is beneficial to the normal use of the secondary battery 100 under normal working conditions, and can 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 change 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.

[0087] In the embodiment of the present application, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃, when the difference in thermal expansion coefficients of the two metal layers is less than 4×10 -6 / ℃, the deformation of the metal sheet 41 during temperature changes is relatively small. When the temperature inside the secondary battery 100 increases, the deformation of the metal sheet 41 may not be sufficient to quickly and effectively open the pressure relief channel, resulting in the failure to release the internal pressure of the secondary battery 100 in time, increasing the safety risk of the secondary battery 100 at abnormally high temperatures. -6 / ℃, the metal sheet 41 will be more sensitive to temperature fluctuations. Even a small temperature fluctuation may cause a large deformation of the metal sheet 41, which may interfere with the normal sealing state of the secondary battery 100 under normal working conditions. -6 / ℃≤G1-G2≤15×10 -6 / °C, which is beneficial to the normal use of the secondary battery 100 and can respond to the temperature change of the secondary battery 100 in time, which is beneficial to the timely pressure relief of the secondary battery 100 under abnormal conditions.

[0088] 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. 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. The metal sheet 41 can work normally within a normal 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 a copper-nickel-chromium-iron combination, a copper-zinc alloy-manganese-copper-nickel combination, a copper-tin-zinc-Invar alloy combination, etc., and its deformation temperature is between 90°C and 150°C, which is conducive to timely pressure relief of the secondary battery 100.

[0089] The synergistic effect between the above-mentioned metal materials can effectively realize the pressure relief function of the secondary battery 100. For example, when the temperature inside the secondary battery 100 rises, the first metal layer 411 will expand relative to the second metal layer 412 due to its large thermal expansion coefficient, so that the metal sheet 41 will bend and deform, and this deformation will act on the seal 42. When the deformation reaches a certain degree, the seal 42 opens, and the pressure inside the secondary battery 100 is released in time.

[0090] Regarding the adjustment of the thermal expansion coefficient of various metal layers, it can be adjusted by adjusting the components of various metal layers. For example, nickel-iron alloy, changing the ratio of nickel and iron will affect the thermal expansion coefficient, and the increase of nickel content will reduce the thermal expansion coefficient. Invar alloy, adding a small amount of other elements such as carbon, silicon, manganese, etc. to Invar alloy will increase the expansion coefficient. Nickel-chromium-iron alloy, adjusting the content of nickel, chromium, iron and other alloy elements can change the thermal expansion coefficient of the alloy. Manganese-copper-nickel alloy, changing the ratio of the three main elements of manganese, copper and nickel can adjust the thermal expansion coefficient. The above-mentioned nickel-chromium-iron alloy, copper-tin-zinc alloy, copper-zinc alloy and alloy steel can adjust the size of their thermal expansion coefficient by adjusting the proportion of each component. For copper, nickel, etc., it can also be adjusted by adding a small amount of other elements, such as adding molybdenum, tungsten, etc. In some other embodiments, the thermal expansion coefficient of various metal layers can also be adjusted by heat treatment, adding trace elements and optimizing processing technology. For example, the thermal expansion coefficient will be different under different heat treatment conditions.

[0091] In the embodiment of the present application, the metal sheet 41 of the memory alloy includes but is not limited to a two-layer metal layer structure, and in some other embodiments, it may also include a three-layer, four-layer or other multi-layer structure. For example, the one with a larger thermal expansion coefficient is regarded as an active layer, and the one with a smaller thermal expansion coefficient is regarded as a passive layer. When the temperature changes, the active layer can bend and deform toward the passive layer, and drive the seal 42 to open.

[0092] Please refer to Figure 5 In an embodiment of the present application, the metal sheet 41 also includes a third metal layer 413, and the third metal layer 413 is stacked between the first metal layer 411 and the second metal layer 412. The third metal layer 413 in the middle can play a buffering role and disperse the stress generated by the first metal layer 411 and the second metal layer 412 during the deformation process. For example, the frequent deformation of the first metal layer 411 and the second metal layer 412 may cause fatigue or damage to the metal sheet 41, and the presence of the third metal layer 413 can extend the service life of the metal sheet 41, allowing it to work more stably. In addition, the regulating effect of the third metal layer 413 in the middle on heat conduction helps to optimize the response speed and accuracy of the pressure relief assembly 40, and more uniform and timely heat conduction can make the metal sheet 41 deform rapidly when the internal temperature of the secondary battery 100 reaches the set value, opening the pressure relief channel.

[0093] In some embodiments, the thermal expansion coefficient of the third metal layer 413 is G3, G2<G3<G1. It can better relieve the stress caused by the first metal layer 411 and the second metal layer 412, and reduce the risk of deformation of the metal sheet 41. Among them, 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 has good toughness and thermal conductivity, which is conducive to the dispersion of stress and the timely transfer of heat.

[0094] In some embodiments, please refer 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, which is communicated 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. The connecting piece 43 can be connected to the housing 10 by welding or bonding.

[0095] The seal 42 is bonded between the connecting sheet 43 and the first metal layer 411, and the metal sheet 41 covers the second through hole 433, so that the metal sheet 41, the seal 42 and the connecting sheet 43 form a whole. During installation, the seal 42 can be first bonded between the metal sheet 41 and the connecting sheet 43, and then the connecting sheet 43 can be connected to the housing 10, which can simplify the installation process and help improve the installation accuracy. During disassembly, the entire pressure relief assembly 40 can be removed from the housing 10 by separating the connecting sheet 43 from the housing 10, so that the pressure relief assembly 40 has a higher integrity, which is conducive to the reuse of the pressure relief assembly 40.

[0096] The inventor of the present application has found that the connecting piece 43 can also be made of a double metal layer memory alloy. Fig. 9 and Fig.10 , along the direction from the first wall surface 121 to the second wall surface 122 (first direction X), the connecting sheet 43 includes a fourth metal layer 431 and a fifth metal layer 432 which are stacked. 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 arranged between the sealing member 42 and the fifth metal layer 432. The thermal expansion coefficient of the fourth metal layer 431 is G4, and the thermal expansion coefficient of the fifth metal layer 432 is G5, G4>G5.

[0097] In the embodiment of the present application, since the thermal expansion coefficient of the fourth metal layer 431 is larger, when the temperature rises due to an abnormal situation in the secondary battery 100, the fourth metal layer 431 expands more. Due to the restriction of the first wall portion 12, the portion of the fourth metal layer 431 located in the center will bulge in the direction away from the first wall portion 12, thereby causing the fourth metal layer 431 to be partially separated from the seal 42, and the bonding force between the connecting piece 43 and the seal 42 is weakened, which is more conducive to the seal 42 being opened, thereby achieving timely release of the internal pressure of the secondary battery 100 and playing a role in pressure relief. In addition, the bending direction of the connecting piece 43 is opposite to that of the metal piece 41, which can further reduce the bonding area between the seal 42 and the metal piece 41 and the connecting piece 43, and further weaken the bonding force, which is conducive to improving the sensitivity of the pressure relief component 40, thereby being able to respond to abnormal temperature changes of the secondary battery 100 in a timely manner.

[0098] Similar to the above-mentioned metal sheet 41, 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.

[0099] In some embodiments, please refer to Fig.11 Alternatively, only the connecting piece 43 may adopt a double-metallic layer memory alloy structure. When an abnormal situation occurs in the secondary battery 100 and causes the temperature to rise, the central portion of the fourth metal layer 431 may protrude away from the first wall portion 12, thereby weakening the bonding force between the connecting piece 43 and the sealing member 42, which is conducive to the sealing member 42 being opened, thereby achieving timely release of the internal pressure of the secondary battery 100.

[0100] Please refer to Figure 12 to Figure 14 , observed from 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 with the first wall portion 12, and 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 arranged around the second region 43a2, and the second region 43a2 is arranged around the first through hole 123. For example, the first region 43a1 is fixed to the first wall portion 12 by welding, and the second region 43a2 does not need to perform any operation and is directly attached to the first wall portion 12, or a partial gap space is preset between the second region 43a2 and the first wall portion 12.

[0101] In the embodiment of the present application, the connecting piece 43 is fixed to the shell 10 only in the first area 43a1 near the edge, and the central part (including the second area 43a2) is relatively free. This structural design provides a certain flexibility for the pressure relief component 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 conform to the bulging deformation of the center of the connecting piece 43, which is conducive to timely pressure relief when the air pressure increases or the temperature changes.

[0102] In some implementations, when viewed from 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 portion of the first through hole 123. When the pressure inside the housing 10 increases, the gas may impact the second portion 43b of the connecting piece 43, which is more conducive to the second portion 43b driving the second area 43a2 to bulge away from the housing 10, thereby partially separating the connecting piece 43 from the sealing member 42, which is conducive to timely responding to the pressure change inside the housing 10, and further reducing the risk of explosion of the secondary battery 100.

[0103] In some embodiments, please refer to Fig.14 , the width of the first area 43a1 is W1, and the width of the second area 43a2 is W2. If the width of the second area 43a2 is too small, it may cause the second area 43a2 to be difficult to protrude in a direction away from the shell 10 in time, which makes it difficult to release the pressure in time. If the width of the second area 43a2 is too large, it may cause the connection strength between the connecting piece 43 and the shell 10 to be insufficient, affecting the sealing performance of the secondary battery 100. In the embodiment of the present application, it is limited to 0.1mm≤W1≤1mm, and it is limited to 1 / 10≤W1 / W2≤1 / 3, for example, 0.3mm≤W1≤3mm, so that the secondary battery 100 has better sealing performance under normal working conditions, and it is beneficial for the secondary battery 100 to make the second area 43a2 protrude in a direction away from the first wall portion 12 under abnormal working conditions, which is more conducive to opening the seal 42, and can facilitate the timely pressure release of the secondary battery 100. The width of the first region 43a1 may be the difference between the outer diameter of the fitting circle where the first region 43a1 is located and the inner diameter of the fitting circle where the first region 43a1 is located, and the second region 43a2 is similar.

[0104] In some embodiments, the connecting piece 43 is in the shape of a ring when viewed from the direction from the first wall 121 to the second wall 122 (first direction X). The ring is a centrally symmetrical figure, and the force can be evenly distributed on the circumference no matter from which direction the pressure acts. The ring-shaped connecting piece 43 can achieve a relatively uniform force when it is subjected to the force transmitted by the internal pressure of the secondary battery 100 and the deformation of the metal sheet 41. For example, when the internal pressure of the secondary battery 100 increases and the gas exerts an outward thrust on the connecting piece 43, the force exerted on each point on the edge of the ring-shaped connecting piece 43 is substantially the same, which reduces the situation of local stress concentration, so that the connecting piece 43 can withstand pressure more stably and is not easily damaged due to excessive local force.

[0105] Moreover, the first through hole 123 is usually circular, and the annular connecting piece 43 can cooperate well therewith, so that the annular connecting piece 43 can 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 (for example, the above-mentioned setting of the first part 43a and the second part 43b) to ensure the timely response of the pressure relief function.

[0106] As for the outer diameter of the connecting piece 43, if the outer diameter is too large, it will occupy more space of the secondary battery 100, affect the thickness of the secondary battery 100, and may cause the energy density loss of the secondary battery 100. If the outer diameter is too small, the connection area between it and the shell 10 is small, and the support for the seal 42 is insufficient. When the internal pressure of the secondary battery 100 changes, the tension and shear force 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.

[0107] In the embodiments of this application, please refer to Fig.15 The outer diameter of the connecting piece 43 is R, 1mm≤R≤6mm, which can reduce the impact on the energy density of the secondary battery 100, and can ensure that the connecting piece 43 and the sealing member 42 have a sufficient connection area, reduce the loosening or falling off of the connecting piece 43, and improve the reliability of the pressure relief assembly 40.

[0108] Preferably, 2 mm ≤ R ≤ 5 mm, which 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, thereby improving the reliability of the pressure relief assembly 40 .

[0109] For the diameter of the first through hole 123, if the diameter is too large, the sealing difficulty will increase, which will increase the risk of electrolyte leakage inside the secondary battery 100, and may cause external air, moisture, etc. to enter the inside of the secondary battery 100, thereby affecting the chemical properties of the electrolyte, and may cause faults such as short circuit inside the secondary battery 100. If the diameter of the first through hole 123 is too small, 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 thermal runaway and short circuit of the battery), the gas cannot be discharged in time, which may cause the shell 10 to rupture or even explode, seriously affecting the safety of the secondary battery 100.

[0110] In the embodiment of the present application, the diameter of the first through hole 123 is R1, 0.5≤R1≤5.5 mm, which can not only reduce the entry of external air, moisture, etc. into the secondary battery 100, but also facilitate the timely discharge of gas.

[0111] As for the diameter of the second through hole 433, if the diameter of the second through hole 433 is too large, it will make it easier for external air, moisture, etc. to enter the interior of the secondary battery 100 through the 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 too small, the gas discharge speed will be limited, resulting in reduced pressure relief efficiency, and it is easy to be blocked. Impurities generated inside the secondary battery 100 (such as tiny particles of electrode materials, solid substances generated by decomposition of electrolyte, etc.) may accumulate at the second through hole 433. Once blocked, the gas cannot be discharged through this channel, resulting in failure of the pressure relief function, thereby affecting the safety of the secondary battery 100.

[0112] In the embodiment of the present 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, etc. into the secondary battery 100, but also reduce the risk of the second through hole 433 being blocked, and is more conducive to the timely discharge of gas.

[0113] Among them, when observed from 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 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 speed to a certain extent and reduce excessive pressure relief. During the normal operation of the secondary battery 100, a small amount of gas will be generated inside, and the generation and consumption of these gases 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 circumstances, 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.

[0114] Furthermore, the area of ​​the second through hole 433 is smaller than that of the pressure relief hole, which can reduce the entry of external air, moisture, etc. into the secondary battery 100. When the pressure is released, the connecting piece 43 can limit the contact between external substances and the electrolyte and electrode materials inside the secondary battery 100, so that the chemical reaction inside the secondary battery 100 can be carried out in a relatively stable environment. Specifically, the area of ​​the second through hole 433 can be selected to be 0.00785mm 2 ≤S2≤16mm 2 .

[0115] In some embodiments, please refer to Fig.16 and Fig.17The pressure relief assembly 40 further includes a protective layer 44, which is disposed on the surface of the second metal layer 412 that is away from the first metal layer 411. The metal sheet 41 may be subjected to external impact, friction, etc. during the production, transportation or use of the secondary battery 100. The protective layer 44 can serve as a buffer layer to absorb and disperse these external forces, reduce scratches, deformation or damage on the metal sheet 41, and improve the stability of the shape and performance of the metal sheet 41.

[0116] As for the material of the protective layer 44, in the embodiment of the present application, the material of the protective layer 44 includes at least one of polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate or polyetheretherketone. Each of the above materials has certain strength and toughness, can withstand certain external forces, and has a good protective effect on the metal sheet 41. In addition, they all have good chemical stability, can resist chemical corrosion to a certain extent, and are conducive to extending the service life of the metal sheet 41.

[0117] Regarding the thickness of the protective layer 44, if the thickness of the protective layer 44 is too large, it may be difficult for the metal sheet 41 to deform in time, affecting the pressure relief function. If the thickness is too small, it is difficult to effectively protect the metal sheet 41. In the embodiment of the present application, along the direction from the first wall 121 to the second wall 122 (the first direction X), the thickness of the protective layer 44 is D2, 0.01mm≤D2≤0.25mm. It can effectively protect the metal sheet 41 and is conducive to the timely deformation of the metal sheet 41 when the temperature changes. Preferably, 0.01mm≤D2≤0.15mm.

[0118] Due to the support of the protective layer 44, the overall strength of the metal sheet 41 can be improved, the risk of deformation under normal working conditions can be reduced, and the pressure relief assembly 40 can have better sealing performance under normal working conditions. Therefore, in the embodiment of the present application, the metal sheet 41 can be appropriately thinned. For example, along the direction from the first wall 121 to the second wall 122 (the first direction X), the thickness of the metal sheet 41 is D1, 0.01mm≤D1≤0.25mm.

[0119] The thinner metal sheet 41 has a shorter heat conduction path. When the temperature inside the secondary battery 100 changes, heat can be transferred more quickly in the metal sheet 41 , so that the metal sheet 41 of the bimetallic layer memory alloy can sense the temperature change more quickly and respond.

[0120] Furthermore, since the thinner metal sheet 41 has lower rigidity, it is less susceptible to interference from factors such as internal stress during its deformation process. 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 assembly 40, thereby improving the accuracy and reliability of the pressure relief process of the secondary battery 100.

[0121] For the sealing member 42 , in the embodiment of the present application, the melting point of the sealing member 42 is T, 90° C.≤T≤150° C.

[0122] Within the normal operating temperature range of the secondary battery 100 (generally -20°C to 85°C), the seal 42 can remain solid and has good sealing performance. It can seal the installation gap between the metal sheet 41 and the shell 10, effectively prevent the electrolyte inside the secondary battery 100 from leaking, and block external air and moisture from entering the interior of the secondary battery 100.

[0123] When the secondary battery 100 has an abnormal situation, such as overcharging, short circuit 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, so that the pressure relief component 40 can be opened in time to reduce the internal pressure of the secondary battery 100 and the explosion. 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 adopts a copper-nickel-chromium-iron combination, a copper-zinc alloy-manganese-copper-nickel combination, a copper-tin-zinc-invar alloy combination, etc., and its deformation temperature is 90°C to 150°C, which can cooperate with the seal 42, which is conducive to the timely pressure relief of the secondary battery 100.

[0124] As for the material of the seal 42, in the embodiment 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. In addition, each material has low permeability to gas and liquid, which can reduce the leakage of the internal electrolyte, and prevent external air, moisture, etc. from entering the interior of the secondary battery 100, which is conducive to maintaining the normal operation of the secondary battery 100.

[0125] As for the adjustment of the melting point of the seal 42:

[0126] The melting point of polypropylene can be adjusted by copolymerization modification: the melting point of polypropylene can be adjusted by copolymerization with a small amount of other monomers. For example, polypropylene modified with ethylene to form ethylene-propylene rubber (EPR). The introduction of ethylene monomer changes the molecular chain structure of polypropylene, reduces the regularity of the molecular chain, reduces the crystallinity, and thus reduces 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 will gradually decrease.

[0127] The melting point of polyethylene can be adjusted by adjusting its density: for example, low-density polyethylene (LDPE), high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) have different melting points.

[0128] The melting point of polyvinylidene fluoride can be adjusted by controlling the crystallinity: by changing the processing conditions, such as stretching, annealing and other processes, the crystallinity can be adjusted, thereby affecting the melting point. For example, annealing at an appropriate temperature can make the crystallization of polyvinylidene fluoride more perfect, the crystallinity is improved, and the melting point is also increased. On the contrary, processing methods such as rapid cooling may reduce the crystallinity, resulting in a lower melting point. The melting point of polyvinylidene fluoride can be adjusted by copolymerization modification.

[0129] The melting point of polytetrafluoroethylene can be adjusted by adding fillers: for example, adding inorganic fillers such as glass fiber and carbon fiber. These fillers can change the thermal properties of the material, such as improving thermal conductivity and making the temperature distribution of the material more uniform during heating. Therefore, it may exhibit different thermal behaviors in actual applications, indirectly affecting its processing performance and performance.

[0130] Regarding the thickness of the seal 42, if the seal 42 is too thick, it may increase the resistance to opening the pressure relief channel, which may cause the pressure relief action to be delayed. If the thickness is too small, it may not provide sufficient sealing force, which may cause electrolyte leakage or external air and moisture to enter the battery.

[0131] In the embodiments of this application, please refer to Fig.17 , along the direction from the first wall 121 to the second wall 122 (first direction X), the thickness of the seal 42 is D3, 0.01mm≤D3≤0.5mm. The sealing performance can be improved when the secondary battery 100 is in normal operation, and the pressure relief channel can be opened in time when the secondary battery 100 is in abnormal condition (pressure increase or temperature increase).

[0132] In the second aspect, the present application also proposes an electronic device, including a secondary battery 100 as in any embodiment of the first aspect described above. The electronic device of the embodiment of the present application is not particularly limited, and it 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, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts, and the like.

[0133] Example 1-1

[0134] Preparation of positive electrode:

[0135] 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 5×10 5) were mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) was added as a solvent, and a positive electrode slurry with a solid content of 75wt% was prepared, and the mixture was stirred evenly in a vacuum mixer. An aluminum foil with a thickness of 8μm and a length of 1000mm was selected as the positive electrode current collector, and the positive electrode slurry was evenly coated on one surface of the positive electrode current collector aluminum foil, and dried at 110°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Afterwards, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer.

[0136] Preparation of negative electrode sheet:

[0137] The negative electrode active material graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-acrylic rubber (SD-3) are mixed in a weight ratio of 89.5:8:1:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness of 5μm and a length of 1050mm is selected as the negative electrode current collector, and the negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil, and dried 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 has been completed. After that, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. A second groove is cleaned out in a negative electrode active material layer by a laser cleaning process, and a part of the negative electrode ear is welded to the negative electrode current collector in the second groove.

[0138] Preparation of isolation membrane:

[0139] Polyethylene is selected as a 7 μm substrate layer, and polyvinylidene fluoride is selected as an adhesive layer. An alumina ceramic layer with a thickness of 2 μm is arranged on the side of the adhesive layer away from the substrate layer to prepare a porous isolation membrane.

[0140] Preparation of electrolyte:

[0141] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt 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.

[0142] Preparation of metal sheets:

[0143] Select thickness D 11 0.15mm copper-zinc alloy (brass) is used as the first metal layer, and the thickness D is selected 12The 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 thermal expansion coefficient G1 of the copper-zinc alloy is (18.5×10 -6 / ℃) is greater than the thermal expansion coefficient of nickel-iron alloy G2 (9.5×10 -6 / ℃).

[0144] Preparation of lithium-ion batteries:

[0145] The positive electrode sheet is welded to the positive electrode ear of the aluminum sheet, and the negative electrode sheet is welded to the negative electrode ear of the nickel sheet. The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain an electrode assembly. The electrode assembly is placed in a steel shell, the positive electrode ear is welded to the pole on the shell, and the negative electrode ear is welded to the shell. The shell has a first through hole, and the diameter R1 of the first through hole is 1mm. After removing moisture at 80°C, the electrolyte is injected, polypropylene is selected as a seal, the metal sheet is bonded to the shell through the seal, and the metal sheet covers the first through hole. After packaging, formation, capacity testing, voltage internal resistance testing and other processes, a lithium-ion battery is obtained.

[0146] Different from 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. In Comparative Example 1-1, a single layer of nickel-iron alloy is used as the metal sheet. In Comparative Example 1-2, two layers of nickel-iron alloy are used as the first metal layer and the second metal layer, that is, G1=G2.

[0147] Conventional working condition test: Stored at 80℃±5℃ for 48 hours, the lithium-ion battery is considered to have passed the test if there is no leakage.

[0148] The thermal shock test process is as follows:

[0149] First, set the test environment temperature to 23℃±2℃ and let the test sample rest for 5 minutes. Then charge the lithium-ion battery sample at a constant current (DC) of 0.2C to a voltage of 3.0V. After completing the above charging operation, let the sample rest for another 5 minutes to allow the lithium-ion battery to have a short stable adjustment period after charging.

[0150] The test furnace temperature was adjusted to 37°C (±2°C), and the lithium-ion battery samples were allowed to rest in the 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 sample performance under the high temperature conditions and in subsequent operations.

[0151] Then charge at a constant current of 1.65C to a voltage of 4.1V, and 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 a voltage of 4.2V, and then switch to constant voltage charging until the current drops to 1.4C. Then 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, 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.

[0152] After completing the above series of complex charging operations, the lithium-ion battery sample was allowed to rest for 5 minutes (Rest 5 min) again.

[0153] Test process: ① Check the appearance before and after the test and take photos; ② Place the temperature sensing wire near the anode ear; ③ Place the lithium-ion battery sample horizontally in the box and heat it to 130±2℃ at a rate of 5±2℃ and maintain it for 30 minutes; ④ Measurement frequency: Use 1KHz specification for voltage and internal resistance measurement, and measure after pretreatment and test; ⑤ Judgment standard: no explosion, no smoke, no fire.

[0154] Each group of 20 lithium-ion batteries undergoes conventional tests and thermal shock tests. Failure in any process is considered a test failure. The number of test failures is N, and the test failure rate is N / 20.

[0155] Table 1

[0156]

[0157]

[0158] According to the above Table 1, in combination with Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-2, in Examples 1-1 to 1-7, the test failure rate 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 memory alloy. Because the thermal expansion coefficient of the first metal layer is larger, when an abnormal condition 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 tilt toward the second metal layer, thereby partially separating the first metal layer from the seal, and the bonding force between the metal sheet and the seal is weakened, which is more conducive to the seal being flushed open, thereby achieving the timely release of the internal pressure of the secondary battery and playing a role in pressure relief.

[0159] 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 the same conditions, the overall failure rate is less 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, and it needs to absorb more heat, which may cause the metal sheet to be difficult to deform and bend in time, and thus make it difficult to release pressure in time. 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 working condition test of the lithium-ion battery, the pressure relief component may be flushed open, resulting in test failure. Therefore, in the embodiments of the present application, the thickness of the metal sheet can be selected to be 0.04mm≤D1≤1mm.

[0160] In Examples 1-1 to 1-7, the test failure rate of Examples 1-1 to 1-5 is less than that of Examples 1-6 to 1-7. In Example 1-6, the thickness of the first metal layer accounts for a relatively large proportion, which may cause the metal sheet to bend excessively, and easily cause the metal sheet to bend when slightly heated, affecting the normal operation of the lithium-ion battery. In Example 1-7, the thickness of the second metal layer is relatively large, which may make it difficult for the first metal layer to drive the second metal layer to deform, and it is also difficult to break the seal, which may make it difficult for the lithium-ion battery to release pressure in time. Similarly, the test failure rate of Examples 1-8 to 1-10 is less than that of Examples 1-11 to 1-12, the test failure rate of Examples 1-13 to 1-15 is less than that of Examples 1-16 to 1-17, the test failure rate of Examples 1-23 to 1-25 is less than that of Examples 1-26 to 1-27, and the test failure rate of Examples 1-28 to 1-30 is less than that of Examples 1-31 to 1-32. Therefore, 1≤D can be selected. 11 / D 12 ≤5.

[0161] Different from Example 1-1, the thermal expansion coefficients of the first metal layer and the second metal layer in Examples 2-1 to 2-30 are different, and the relevant parameters are shown in Table 2 below.

[0162] Table 2

[0163]

[0164]

[0165] According to Table 2 above, in Examples 2-2 to 2-5, the test failure rate is less than that in Examples 2-1 and 2-6. In Example 2-1, the difference in the thermal expansion coefficients between the first metal layer and the second metal layer is small, which may result in a small deformation of the metal sheet, which may not be sufficient to quickly and effectively open the pressure relief channel. In Example 2-6, the difference in the thermal expansion coefficients between the first metal layer and the second metal layer is large, which may result in excessive bending of the metal sheet, that is, the metal sheet is prone to bend quickly, which may cause the metal sheet to fail quickly. In Examples 2-2 to 2-5, the difference in the thermal expansion coefficients between the first metal layer and the second metal layer is better, which is conducive to the normal use of the lithium-ion battery under normal working conditions, and can respond to the temperature changes of the lithium-ion battery in a timely manner, which is conducive to the timely pressure relief of the lithium-ion battery under abnormal conditions. Similarly, in Examples 2-8 to 2-11, the test failure rate is less than that in Examples 2-7 and 2-12, in Examples 2-14 to 2-17, the test failure rate is less than that in Examples 2-13 and 2-18, in Examples 2-20 to 2-23, the test failure rate is less than that in Examples 2-19 and 2-24, and in Examples 2-26 to 2-29, the test failure rate is less than that in Examples 2-25 and 2-30. Therefore, in the embodiments of the present application, 4×10 -6 / ℃≤G1-G2≤15×10 -6 / ℃.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the 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 first wall portion being provided with a first through 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 first through 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>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, 0.04 mm≤D1≤1 mm.

3. The secondary battery according to claim 2, 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.

4. 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.

5. The secondary battery according to claim 1, characterized in that: The metal sheet further includes a third metal layer 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 thermal expansion coefficient of the third metal layer is G3, 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 claim 1, characterized in that: The pressure relief assembly also includes a connecting sheet arranged on the first wall surface, the connecting sheet is provided with a second through hole, the second through hole is communicated with the first through hole, the sealing member is bonded between the connecting sheet 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 R, 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, 0.5≤R1≤5.5mm; The diameter of the second through hole is R2, 0.1 mm≤R2≤4 mm.

17. 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 area of ​​the first through hole is S1, and the area of ​​the second through hole is S2, S2<S1, 0.00785mm 2 ≤S2≤16mm 2 .

18. The secondary battery according to claim 1, characterized in that: The pressure relief assembly further includes a protective layer, which is disposed on a surface of the second metal layer facing away from 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, 0.01 mm≤D1≤0.25 mm.

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, 0.01 mm≤D2≤0.25 mm.

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 material of the protective layer includes at least one of polyethylene terephthalate, polyamide, polypropylene, polyethylene, polyimide, polyvinyl chloride, polystyrene, polyurethane, polycarbonate or polyetheretherketone.

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

24. 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 sealing member is D3, and 0.01 mm≤D3≤0.5 mm.

25. 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.

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

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