Secondary battery, battery pack, and electronic device

Abstract

The invention provides a secondary battery, a battery pack and an electronic device. The secondary battery comprises a shell and an electrode assembly, the shell comprises an end wall and a side wall surrounding the end wall, and the side wall and the end wall are integrally stretched and formed; the electrode assembly is accommodated in the shell; wherein the wall thickness of the end wall is a, the wall thickness of the side wall is b, and a / b is greater than 1 and less than 3, so that the technical problem of battery performance degradation caused by non-uniform pressure of the shell on the side surface of the electrode assembly can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery, a battery pack and an electronic device. Background Art

[0002] At present, cylindrical batteries are widely used in various industries due to their advantages such as mature production technology, high yield rate, low processing cost, good safety performance and heat dissipation performance.

[0003] To increase the capacity density of battery casings, current manufacturing processes strive to make the casing sidewalls as thin as possible, providing more space for the active materials inside the battery and thereby increasing the battery's energy density. However, this pursuit of thin sidewalls reduces the casing's cylindricity. This reduction in casing cylindricity manifests as fluctuations in the casing's axial diameter, leading to uneven lateral pressure on the electrode assembly, degrading battery performance, and affecting battery consistency. Summary of the Invention

[0004] The present invention provides a secondary battery, a battery pack and an electronic device to improve the technical problem of battery performance degradation caused by uneven pressure of a shell on the side of an electrode assembly.

[0005] To achieve the above and other related objectives, the present invention provides a secondary battery, a battery pack, and an electronic device. The secondary battery comprises a housing and an electrode assembly; the housing comprises an end wall and a side wall surrounding the end wall, the side wall and the end wall being integrally formed by stretching; the electrode assembly is housed within the housing; the end wall has a thickness a, the side wall has a thickness b, and 1 < a / b < 3.

[0006] In the above technical solution, the end wall is not stretched or the degree of stretching is very small, so the wall thickness of the end wall is approximately equal to the thickness of the raw material. By limiting the ratio between the end wall thickness and the side wall thickness within the range of 1<a / b<3, the radial dimension of the shell perpendicular to the stretching direction along the height direction of the shell will not fluctuate too much during the gradual thinning process of multiple stretching, which is beneficial to the consistency of the finished shell. In addition, the shell has a more uniform pressure on the side of the electrode assembly to optimize the performance of the secondary battery.

[0007] In an example of the secondary battery of the present invention, 1.3≤a / b≤2.

[0008] In the above technical solution, 1.3≤a / b≤2 is further limited, which can not only further reduce the fluctuation of the radial dimension of the shell along the height direction of the shell, but also is beneficial to the balance between the strength and weight of the shell, so as to achieve the effect of both lightweight and high strength of the shell, thereby improving the safety of the battery.

[0009] In an example of the secondary battery of the present invention, the secondary battery is a cylindrical battery, the diameter of the end wall is D, the height of the side wall is L, and 1.5≤L / D≤3.5.

[0010] In the above technical solution, the limitation of 1.5≤L / D≤3.5 is conducive to the balance between the capacity and cylindricity of the shell, and can achieve the effect of the shell having a higher capacity and a higher cylindricity, thereby improving the consistency of the battery.

[0011] In an example of the secondary battery of the present invention, the diameter of the end wall is in the range of 30 mm ≤ D ≤ 50 mm.

[0012] In the above technical solution, the limitation of 30mm≤D≤50mm can achieve that the shell has a larger capacity while meeting the strength requirements of the electrode assembly for the shell, thereby improving the safety performance of the battery.

[0013] In an example of the secondary battery of the present invention, the secondary battery is a cylindrical battery, and the tolerance of the diameter of the shell is less than or equal to 0.07 mm.

[0014] In the above technical solution, the limitation of the tolerance of the shell diameter can achieve higher assembly accuracy and sealing performance of the shell and more uniform pressure on the side of the electrode assembly, thereby improving assembly efficiency and safety of the secondary battery.

[0015] In an example of the secondary battery of the present invention, the secondary battery is a cylindrical battery, and the roundness of the shell is less than or equal to 0.09 mm.

[0016] In the above technical solution, the limitation on the roundness of the shell can achieve better consistency of the shell, more uniform pressure on the side of the electrode assembly, optimize thermal management efficiency and improve sealing performance, thereby improving the safety and reliability of the shell.

[0017] In an example of a secondary battery of the present invention, an electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator stacked and wound to form a winding body, the winding axis of the winding body is perpendicular to the end wall, the negative electrode sheet is coated with a negative electrode active material layer, the Si content in the negative electrode active material layer is greater than 2%, and the Vickers hardness of the side wall is greater than or equal to 160HV.

[0018] In the above technical solution, the Vickers hardness of the side wall is greater than or equal to 160HV, which can provide better structural support to protect the internal components of the battery from external impact and pressure, reduce the deformation of the side wall during battery charging and discharging, better resist internal pressure, and also have high wear resistance.

[0019] In an example of the secondary battery of the present invention, the secondary battery further includes a pole, a pole hole is provided on the end wall, the pole passes through the pole hole and is insulated and fixed to the end wall, the pole is electrically connected to the positive electrode sheet, and the Vickers hardness of the end wall is greater than 100HV and less than 150HV.

[0020] In the above technical solution, the Vickers hardness of the end wall is greater than the limit of 100HV, so that the end wall has sufficient hardness to provide better structural support. The limit is less than 150HV, so that the hardness of the end wall is less than the hardness of the side wall. When the internal pressure of the battery is too high, the end wall is more likely to deform, which helps to guide the pressure to be released through the pole hole at the end wall, thereby improving the safety performance of the battery.

[0021] In an example of a secondary battery of the present invention, the shell is electrically connected to the negative electrode plate, the outer side of the end wall is used to be welded to the external bus bar, and a first nickel plating layer is provided on the outer side of the shell, and the thickness of the first nickel plating layer located on the end wall is greater than the thickness of the first nickel plating layer located on the side wall.

[0022] In the above technical solution, the first nickel plating layer can improve the corrosion resistance, wear resistance and rust resistance of the outer side of the shell, and can also enhance the surface hardness of the shell, which helps to protect the internal components of the battery. The first nickel plating layer can also improve the welding performance of the shell, which is beneficial to the welding connection with other external components. The outer side of the end wall is used for welding with the external bus bar. The thicker thickness of the first nickel plating layer located on the end wall can play a soldering effect and can also improve the corrosion resistance, rust resistance and wear resistance of the first nickel plating layer, so as to help the end wall adapt to complex working conditions. The thinner thickness of the first nickel plating layer located on the side wall can reduce costs while meeting the corrosion resistance, rust resistance and wear resistance. In addition, it can also prevent the uneven thickness or even local corrosion caused by the first nickel plating layer being easily peeled off when worn.

[0023] In an example of the secondary battery of the present invention, the thickness of the first nickel plating layer on the end wall is c, the thickness of the first nickel plating layer on the side wall is d, and 1<c / d<3.

[0024] In the above technical solution, by limiting the ratio between the first nickel-plated layer located on the end wall and the first nickel-plated layer located on the side wall to satisfy 1<c / d<3, the corrosion resistance, rust resistance and wear resistance of the first nickel-plated layer are further optimized. In addition, when adopting the pre-nickel-plating process, it can also be limited that the stretching ratio of the first nickel-plated layer located on the side wall will not be too high, thereby reducing the possibility of the first nickel-plated layer being broken, preventing pitting corrosion, and thereby improving the corrosion resistance and wear resistance of the first nickel-plated layer.

[0025] In an example of the secondary battery of the present invention, the thickness of the first nickel plating layer on the end wall ranges from 4 μm to 5 μm, and the thickness of the first nickel plating layer on the side wall ranges from 2 μm to 4 μm.

[0026] In the above technical solution, the thickness range of the first nickel plating layer located on the end wall and the first nickel plating layer located on the side wall is further limited, which further optimizes the corrosion resistance, rust resistance and wear resistance of the first nickel plating layer, and reduces costs while meeting the corrosion resistance, rust resistance and wear resistance.

[0027] In an example of a secondary battery of the present invention, an insulating member is provided between the end wall and the electrode assembly to isolate the end wall and the electrode assembly, a second nickel plating layer is provided on the inner side of the shell, and the thickness of the second nickel plating layer on the end wall is greater than the thickness of the second nickel plating layer on the side wall.

[0028] In the above technical solution, the second nickel plating layer located on the end wall is set to be thicker, which can overcome the liquid phase corrosion caused by the residual electrolyte between the end wall and the insulating part. The second nickel plating layer located on the side wall is set to be thinner. On the one hand, it can reduce costs while meeting the requirements of corrosion resistance, rust resistance and wear resistance. On the other hand, it can reduce the amount of the first nickel plating layer falling off, thereby improving the corrosion resistance of the second nickel plating layer and improving the safety performance of the battery.

[0029] In an example of the secondary battery of the present invention, the thickness of the second nickel plating layer on the end wall is e, the thickness of the second nickel plating layer on the side wall is f, and 1<e / f<3.

[0030] In the above technical solution, by limiting the ratio between the second nickel-plated layer located on the end wall and the second nickel-plated layer located on the side wall to satisfy 1<e / f<3, the corrosion resistance, rust resistance and wear resistance of the second nickel-plated layer are further optimized. In addition, when adopting the pre-nickel-plating process, the stretching ratio of the second nickel-plated layer located on the side wall can also be limited to not be too high, thereby reducing the possibility of the second nickel-plated layer being broken, preventing pitting corrosion, and thereby improving the corrosion resistance and wear resistance of the first nickel-plated layer.

[0031] In an example of the secondary battery of the present invention, the thickness of the second nickel plating layer on the end wall ranges from 2 μm to 3 μm, and the thickness of the second nickel plating layer on the side wall ranges from 1 μm to 2 μm.

[0032] In the above technical solution, the thickness range of the second nickel plating layer located on the end wall and the second nickel plating layer located on the side wall is further limited, which further optimizes the corrosion resistance of the second nickel plating layer and reduces costs while meeting the corrosion resistance.

[0033] In an example of the secondary battery of the present invention, along the same thickness direction of the shell, the thickness of the first nickel plating layer is greater than the thickness of the second nickel plating layer.

[0034] In the above technical solution, the thickness of the first nickel plating layer located on the outside of the shell is set to be thicker, which can improve the wear resistance, corrosion resistance and rust resistance of the outside of the shell, so that the shell can adapt to the complex external working environment; the thickness of the second nickel plating layer located on the inside of the shell is set to be thinner, which can reduce the risk of nickel falling off. If metal powder remains inside the battery, it may cause micro-short circuits and increase the risk of thermal runaway of the battery. This setting can improve the safety performance of the battery while achieving the corrosion resistance effect on the inside of the shell.

[0035] In an example of a secondary battery of the present invention, the end wall and the side wall are connected by a transition portion, and the transition portion includes a first rounded corner connecting the outer surface of the end wall and the outer surface of the side wall and a second rounded corner connecting the inner surface of the end wall and the inner surface of the side wall, the radius of the first rounded corner is r1, the radius of the second rounded corner is r2, r1 / a≥1, r2 / a≥1.

[0036] In the above technical solution, the setting of the transition portion and the limitation of r1 / a≥1, r2 / a≥1 can achieve a smooth transition from the end wall to the side wall. On the one hand, it can prevent tensile fracture caused by sharp transition. On the other hand, when using the pre-nickel plating process, it can also reduce the shedding of the nickel plating layer during the side wall stretching process. On the other hand, it can also alleviate the stress concentration at the corners of the end wall and the side wall.

[0037] In an example of the secondary battery of the present invention, 0.8≤(r1-r2) / a≤0.95.

[0038] In the above technical solution, the ratio of the thickness of the transition portion to the thickness of the end wall is limited to the above range, which can achieve a slow transition between the end wall and the transition portion. On the one hand, it can prevent tensile fracture caused by drastic transition. On the other hand, when using the pre-nickel plating process, it can also reduce the shedding of the nickel plating layer during the side wall stretching process.

[0039] In an example of the secondary battery of the present invention, the transition portion is gradually stretched along the axial direction of the side wall from the inner surface of the end wall facing the interior of the shell to be equal to the wall thickness of the side wall, and the stretching height of the transition portion is h, 0.5≤r1 / h≤1.

[0040] In the above technical solution, the ratio of the first fillet radius to the stretching height is limited to 0.5 ≤ r1 / h ≤ 1. r1 / h ≥ 0.5 can achieve a smooth transition from the end wall to the side wall. On the one hand, it can prevent tensile fracture caused by a sharp transition. On the other hand, when using a pre-nickel plating process, it can also reduce the shedding of the nickel plating during the side wall stretching process. On the other hand, it can also alleviate stress concentration at the corners of the end wall and side wall. The limitation of R1 / h ≤ 1 can prevent the internal components of the battery from interfering with the transition portion when entering the shell.

[0041] In an example of the secondary battery of the present invention, 1 mm ≤ r1 ≤ 1.5 mm, and 1 mm ≤ h ≤ 2 mm.

[0042] In the above technical solution, the first fillet radius and the stretching height are within the above range, which can achieve a smooth transition from the end wall to the side wall on the one hand, and prevent the internal components of the battery from interfering with the transition part when entering the shell on the other hand.

[0043] In an example of a secondary battery of the present invention, an electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a wound body formed by stacking and winding a separator. The positive electrode sheet includes a first coating area coated with a positive electrode active material and a first uncoated area not coated with the positive electrode active material. The negative electrode sheet includes a second coating area coated with a negative electrode active material and a second uncoated area not coated with the negative electrode active material. Along the axial direction of the electrode assembly, the electrode assembly includes a reaction area and two non-reactive areas located on both sides of the reaction area. The reaction area is the portion where the first coating area and the second coating area overlap along the radial direction of the electrode assembly. The non-reactive area is the portion where only the first coating area or only the second coating area is present. The distance from the boundary line between the non-reactive area and the reaction area close to the end wall to the inner side of the end wall is g, and g≥h.

[0044] In the above technical solution, during the charge and discharge process of the battery, since the first coating area and the second coating area in the reaction area of ​​the electrode assembly overlap along the radial direction of the electrode assembly, the reaction area expands cumulatively in the radial direction, the expansion force is large, and a large pressure is applied to the side wall. However, the non-reactive area of ​​the electrode assembly does not expand because it only has the first coating area or the second coating area. Therefore, the distance from the boundary line between the non-reactive area and the reaction area to the inner side of the end wall is limited to be greater than the stretching height of the transition part. This can ensure that the reaction area does not overlap with the transition part, that is, it is located at a place where the wall thickness of the side wall is relatively uniform. This can prevent the reaction area from pressing the transition part first when expanding, causing the shell to break at the transition part. At the same time, the pressure applied to the side wall when the electrode assembly expands can be uniform, thereby improving the safety performance of the battery.

[0045] In an example of the secondary battery of the present invention, the shell is a steel shell.

[0046] In the above technical solution, the steel shell has excellent properties of wear resistance, corrosion resistance, dust resistance and waterproofness, and can provide better protection.

[0047] In one example of a secondary battery of the present invention, an end of the side wall away from the end wall has an opening, and an end of the side wall close to the opening includes a rolling groove recessed toward the interior of the shell, the rolling groove forms a bulge inside the side wall, and the open end of the side wall is bent toward the center of the shell to form a flange; the secondary battery also includes an end cover, which is sealed and installed between the bulge and the flange.

[0048] In the above technical solution, the end cover is sealed and installed by rolling grooves, which is beneficial to improving the sealing strength, improving production efficiency, improving the sealing performance and improving the battery energy density.

[0049] The present invention also provides a battery pack, which includes any one of the above secondary batteries.

[0050] The present invention also provides an electronic device, which includes the battery pack.

[0051] In the secondary battery of the present invention, the end wall is not stretched or is stretched to a very small extent, so the wall thickness of the end wall is approximately equal to the thickness of the raw material. By limiting the ratio between the wall thickness of the end wall and the wall thickness within the range of 1<a / b<3, the radial dimension of the shell perpendicular to the stretching direction along the height direction of the shell will not fluctuate too much during the gradual thinning process of the shell through multiple stretching, which is beneficial to the consistency of the finished shell. In addition, it is achieved that the shell exerts a relatively uniform pressure on the side of the electrode assembly to optimize the performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 This is a schematic structural diagram of an embodiment of a secondary battery of the present invention;

[0054] Figure 2 This is a schematic structural diagram of a housing of a secondary battery according to an embodiment of the present invention;

[0055] Figure 3 for Figure 1 A partial enlarged view of point A in the middle;

[0056] Figure 4 is a single value diagram of the shell diameter at different positions;

[0057] Figure 5 is a cross-sectional view of an electrode assembly in one embodiment of a secondary battery of the present invention;

[0058] Figure 6 for Figure 2 A partial enlarged view of the shell part at B in the middle;

[0059] Figure 7 is a schematic diagram of an embodiment of a battery pack of the present invention;

[0060] Figure 8 is a schematic diagram of an electronic device according to an embodiment of the present invention;

[0061] Figure 9 This is a schematic structural diagram of a square shell battery in one embodiment of a secondary battery of the present invention;

[0062] Figure 10 1 is a cross-sectional view of a square shell battery in one embodiment of a secondary battery of the present invention.

[0063] Component number description

[0064] 1. Electronic device; 10. Battery pack; 11. Working unit; 101. Box; 102. Box cover; 100. Secondary battery; 110. Housing; 111. End wall; 112. Side wall; 113. Opening; 114. First nickel plating layer; 115. Second nickel plating layer; 116. Transition portion; 1161. First fillet; 1162. Second fillet; 120. Electrode assembly; 121. Positive electrode sheet; 1211. Positive electrode current collector; 1212, first coating area; 1213, first uncoated area; 122, separator; 123, negative electrode pole piece; 1231, negative electrode current collector; 1232, second coating area; 1233, second uncoated area; 124, positive electrode tab; 125, negative electrode tab; 126, wound body; 127, reaction area; 128, non-reaction area; 130, pole; 140, end cover; 150, insulating member. DETAILED DESCRIPTION

[0065] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following examples and the features in the examples can be combined with each other unless they conflict. It should also be understood that the terms used in the examples of the present invention are for the purpose of describing specific embodiments, not for the purpose of limiting the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under the conditions recommended by the manufacturers.

[0066] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. Unless otherwise defined, all technical and scientific terms used herein are consistent with the prior art as understood by those skilled in the art and the description of the present invention. Any prior art methods, devices, and materials similar or equivalent to those in the examples of the present invention may also be used to implement the present invention.

[0067] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0068] A secondary battery includes an electrode assembly, which is a component where electrochemical reactions occur in the secondary battery and may include one or more electrode assemblies.

[0069] The secondary battery also includes a shell, an end cover and a pole. The shell includes an end wall and a side wall surrounding the end wall. The end wall and the side wall are stretched and formed as one piece. One end of the side wall has an opening. The electrode assembly can be assembled into the shell through the opening of the shell. The end cover is used to cover the opening of the shell to achieve sealing. The pole passes through the end wall and is electrically connected to the electrode assembly to conduct the electrical energy generated by the electrode assembly.

[0070] Secondary batteries utilize an electrode assembly assembled within a steel casing. The casing isolates the battery from the external environment, protecting the electrochemical reactions of the active materials within. The casing's sidewalls also significantly constrain radial expansion of the electrode assembly. As battery performance requirements increase, current manufacturing processes are focused on making the sidewalls as thin as possible to increase the capacity density of steel casings. This design reduces the weight of the steel casing, freeing up space for the active materials within the battery, thereby increasing the battery's energy density.

[0071] However, the inventors discovered that this pursuit of thin sidewalls may also bring some potential problems, especially since the sidewalls and end walls are stretched and formed as one piece. As the stretching ratio increases, the thickness of the shell sidewalls relative to the end walls gradually decreases. Along the height direction of the shell, the fluctuation of the radial dimension of the shell perpendicular to the stretching direction will increase, causing uneven lateral pressure of the shell on the electrode assembly, resulting in degradation of battery performance and affecting the consistency of the battery. Therefore, during the design and manufacturing process, it is necessary to find a balance between improving the capacity density and ensuring sufficient radial dimensions of the shell.

[0072] In view of this, the present invention provides a technical solution. During the stretching process of the shell, by controlling the stretching ratio of the end wall and the side wall within the range of 1<a / b<3, the shell is gradually thinned during multiple stretching. The radial dimension of the shell perpendicular to the stretching direction along the height direction of the shell will not fluctuate too much, which is beneficial to the consistency of the finished shell and makes the shell have a more uniform pressure on the side of the electrode assembly.

[0073] See also Figures 1 to 10 The present invention provides a secondary battery 100 , which includes a shell 110 , an electrode assembly 120 , a pole 130 and an end cover 140 .

[0074] See also Figure 1 and Figure 2 The shell 110 includes an end wall 111 and a side wall 112 surrounding the end wall 111. The side wall 112 and the end wall 111 are stretched and formed as a whole. The stretching process is a stamping processing method that uses a stretching die to press a sheet blank into a hollow part with various openings 113. Specifically, in this embodiment, a suitable die is first selected according to the target shape of the shell 110. For example, the shape of the shell 110 can be a square shell, a cylindrical shell or a polygonal prismatic shell, etc., and then the blank is stamped. The first step is to stamp out the prototype of the end wall 111, the side wall 112 and the cavity. In order to ensure the reliability of the stretching and avoid stretching fracture, it is necessary to replace the dies of different sizes multiple times and stamp multiple times until the stretching is to the preset size.

[0075] In some embodiments, the housing 110 may be in the shape of a square shell. Figure 9 and Figure 10 In this embodiment, please refer to Figure 1 The outer edge of the end wall 111 is circular, and the side wall 112 is cylindrical and surrounds the outer edge of the end wall 111, and a circular opening 113 is formed at the end of the side wall 112 away from the end wall 111. A accommodating cavity is formed in the shell 110 surrounded by the end wall 111 and the side wall 112, which is used to accommodate the electrode assembly 120, electrolyte and other necessary battery components. Specifically, the diameter of the shell 110 can be determined according to the specific size of the electrode assembly 120, such as 18mm, 21mm, 46mm, etc. The material of the shell 110 can be various, for example, copper, iron, aluminum, steel, aluminum alloy, etc. In order to prevent the shell 110 from rusting during long-term use, a layer of rust-proof material such as metal nickel can be plated on the surface of the shell 110.

[0076] See also Figure 2 and Figure 3In this embodiment, the end wall 111 is only stamped in the first step and is not subsequently stretched. Therefore, the wall thickness of the end wall 111 is approximately equal to the thickness of the raw material, i.e., the blank, while the side wall 112 needs to be stamped multiple times until it is stretched to a preset size. Specifically, the wall thickness of the end wall 111 is a, and the wall thickness of the side wall 112 is b. It should be noted that during stamping and stretching, sudden changes in size can easily lead to stress concentration, reduced elongation at break, and reduced structural strength. Therefore, the size of the shell 110 is usually variable in thickness. In this embodiment, In this embodiment, the wall thickness a of the end wall 111 is measured as follows: first, the thickness is measured at 5 points on the circumference of 1 / 2 diameter of the end wall 111, and then the average value of the 5 values ​​is obtained; the wall thickness b of the side wall 112 is measured as follows: first, the thickness at 1 / 3 height, 1 / 2 height and 2 / 3 height of the side wall 112 is measured respectively. Specifically, the thickness is measured at 5 points on the circumference of each height, and then the average value is obtained to obtain the thickness at each height, and then the average value of the thickness at these three heights is obtained.

[0077] The inventors found that during the stamping and stretching process of the housing 110, the bottom of the stamping die has a large constraint, so the size of the bottom is relatively stable, while the middle part has no strong constraint, so a concave phenomenon may occur during the stamping process. Figure 4 As shown, Figure 4 Taking a cylindrical battery with a diameter of 46 mm and a height of 120 mm as an example, the diameter values ​​of the shell 110 at 5 mm, 60 mm, and 115 mm from the opening 113 respectively show that the diameter of the middle portion of the shell 110 is smaller than the diameters at the two ends of the shell 110. Furthermore, if the stretching ratio of the side wall 112 is greater, the cumulative amount of indentation will increase, resulting in uneven diameter of the shell 110 and affecting the consistency of the shell 110. Therefore, the ratio range of the end wall 111 to the wall thickness is limited to: 1 < a / b < 3, which can limit the stretching ratio of the side wall 112 to not too high, so that the diameter and cylindricity of the shell 110 will not fluctuate too much during the gradual thinning process of multiple stretching. This is beneficial to the consistency of the finished shell 110 and ensures that the shell 110 exerts a more uniform pressure on the side of the electrode assembly 120, thereby optimizing the performance of the secondary battery 100.

[0078] See also Figure 1 、 Figure 3 and Figure 5The electrode assembly 120 is housed in the housing 110. The electrode assembly 120 is a component where electrochemical reactions occur in the secondary battery 100. The housing 110 may contain one or more electrode assemblies 120. The electrode assembly 120 includes a positive electrode sheet 121, a negative electrode sheet 123, and a separator 122 stacked and wound to form a wound body 126. Specifically, the positive electrode sheet 121 includes a positive electrode collector 1211 and a positive electrode active material. The positive electrode active material is coated on the surface of the positive electrode collector 1211; the positive electrode collector 1211 includes a first coated area 1212 coated with the active material and a first uncoated area 1213 not coated with the active material. The first uncoated area 1213 is located at the end of the positive electrode sheet 121. The other end of the first uncoated area 1213 extends out of the separator 122 along the winding axis of the electrode assembly 120 and is bent toward the winding axis to form a positive electrode tab 124. The negative electrode sheet 123 includes a negative electrode current collector 1231 and a negative electrode active material, and the negative electrode active material is coated on the surface of the negative electrode current collector 1231; the negative electrode current collector 1231 includes a second coated area 1232 coated with the active material and a second uncoated area 1233 not coated with the active material, and the second uncoated area 1233 is located at the end of the negative electrode sheet 123, and the second uncoated area 1233 extends out of the separator 122 along the winding axis direction of the electrode assembly 120 and is bent toward the winding axis to form a negative electrode tab 125.

[0079] See also Figure 1 、 Figure 3 and Figure 5 The separator 122 is disposed between the positive electrode sheet 121 and the negative electrode sheet 123 to separate the positive electrode active material layer from the negative electrode active material layer. Taking the lithium-ion secondary battery 100 as an example, the material of the positive electrode current collector 1211 can be aluminum, and the positive electrode active material layer includes a positive electrode active material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The material of the negative electrode current collector 1231 can be copper, and the negative electrode active material layer includes a negative electrode active material, which can be carbon or silicon. The base material of the separator 122 can be polypropylene (PP) or polyethylene (PE), etc. To protect and insulate the electrode assembly 120, an insulating film can also be coated on the outside of the electrode assembly 120. The insulating film can be synthesized from PP, PE, polyethylene terephthalate (PET), polyvinyl chloride (PVC), or other polymer materials.

[0080] See also Figure 1 、 Figure 3 and Figure 5Furthermore, in the present invention, the positive electrode tab 124 faces the end wall 111 or the opening 113, while the negative electrode tab 125 faces the other end of the housing 110. In this embodiment, the positive electrode tab 124 faces the end wall 111 and is electrically connected to the pole 130, causing the pole 130 to be positively charged. The negative electrode tab 125 faces the opening 113, and the housing 110 is electrically connected to the negative electrode tab 125, causing the housing 110 to be negatively charged. However, in other embodiments, the negative electrode tab 125 may be connected to the pole 130, while the positive electrode tab 124 is connected to the housing 110.

[0081] See also Figure 1 In this embodiment, the secondary battery 100 further includes a pole 130. Specifically, the pole 130 passes through the end wall 111 and is insulated from the end wall 111. One end of the pole 130 facing the electrode assembly 120 passes through the end wall 111 to be directly electrically connected to the positive electrode tab 124 or electrically connected through an indirect transfer. The structure of the pole 130 can be any suitable form that can pass through the end wall 111 and be electrically connected to the positive electrode tab 124 of the electrode assembly 120. For example, the cross-section can be circular, square, prismatic, or a special-shaped profile that can achieve stable conductivity. The hole in the pole 130 corresponds to the shape of the pole 130. In this embodiment, the cross-section of the pole 130 is circular.

[0082] See also Figure 1 In this embodiment, the secondary battery 100 further includes an end cap 140, which is sealingly mounted to the opening 113. The outer edge of the end cap 140 corresponds in shape to the opening 113 and is connected to the side wall 112 to seal the opening 113. In a specific embodiment, the end of the side wall 112 near the opening 113 includes a rolling groove recessed into the interior of the housing 110. The rolling groove is capable of limiting the axial displacement of the electrode assembly 120. The rolling groove forms a protrusion within the side wall 112, and the open end of the side wall 112 is bent toward the center of the housing 110 to form a flange. The end cap 140 is sealingly mounted between the protrusion and the flange. Specifically, a sealing ring is provided between the end cap 140 and the side wall 112. The edge of the opening 113 is sealed so that the end cap 140 presses against the sealing ring, forming a reliable connection.

[0083] In an example of the secondary battery 100 of the present invention, 1.3≤a / b≤2 is further limited, for example, it can be 1.3, 1.5, 1.6, 1.7, 1.8 or 2; the shell 110 that meets this limitation can not only further reduce the fluctuation of the radial size of the shell 110, but also, since the larger a / b is, the lighter the shell 110 is at the same radial size and height, the more conducive to lightweighting and cost reduction. However, if a / b is too large, the side wall 112 will be too thin, which is more likely to break when the secondary battery 100 is subjected to height pressure or side puncture. Therefore, the limitation of this range is conducive to the balance between the strength and weight of the shell 110, so as to achieve the effect of both lightweighting and having high strength of the shell 110, thereby improving the safety of the battery.

[0084] See also Figure 2 In an example of a secondary battery 100 of the present invention, the secondary battery 100 is a cylindrical battery, the diameter of the end wall 111 is D, the height of the side wall 112 is L, and 1.5≤L / D≤3.5. For example, it can be 1.5, 2, 2.5, 3, or 3.5. A larger L / D value means that for the same diameter, the height of the housing 110 is higher, the size of the electrode assembly 120 that can be accommodated is larger, and the battery capacity is greater. However, a higher height also means that the housing 110 is stamped and stretched more times, and the cumulative amount of indentation generated during the stamping process is greater, resulting in uneven diameter of the housing 110, that is, reducing the cylindricity of the housing 110 and affecting the consistency of the housing 110. Therefore, the limitation of 1.5≤L / D≤3.5 is conducive to balancing the capacity and cylindricity of the housing 110, and can achieve the effect of having both higher capacity and higher cylindricity of the housing 110, thereby improving the consistency of the battery.

[0085] See also Figure 2 In an example of the secondary battery 100 of the present invention, the diameter of the end wall 111 is in the range of 30mm≤D≤50mm. For example, it can be 30, 32, 36, 40, 42, 46, or 50. The larger the value of D, the greater the capacity of the housing 110, and the larger the diameter of the electrode assembly 120 accommodated. However, if D is too high, the diameter of the electrode assembly 120 will be too large, resulting in excessive accumulation of expansion force, which will put a greater test on the strength of the housing 110. The larger the diameter of the electrode assembly 120, the greater the difficulty of heat dissipation. Therefore, the limit of 30mm≤D≤50mm can achieve a larger capacity for the housing 110 while meeting the strength requirements of the electrode assembly 120, thereby improving the safety performance of the battery.

[0086] See also Figure 2In an example of a secondary battery 100 according to the present invention, the secondary battery 100 is a cylindrical battery, and the diameter tolerance of the housing 110 is less than or equal to 0.07 mm. This tolerance on the diameter of the housing 110 ensures high assembly precision and sealing performance, as well as uniform pressure on the sides of the electrode assembly 120, thereby improving assembly efficiency and the safety of the secondary battery 100.

[0087] See also Figure 2 In an example of a secondary battery 100 according to the present invention, the secondary battery 100 is a cylindrical battery, and the roundness of the housing 110 is less than or equal to 0.09 mm. This defined roundness of the housing 110 ensures better consistency of the housing 110, applies more uniform pressure to the sides of the electrode assembly 120, optimizes thermal management efficiency, and improves sealing performance, thereby enhancing the safety and reliability of the housing 110.

[0088] See also Figure 2 and 5 In an example of a secondary battery 100 according to the present invention, the electrode assembly 120 includes a positive electrode sheet 121, a negative electrode sheet 123, and a separator 122 stacked and wound to form a jellyroll 126. The winding axis of the jellyroll 126 is perpendicular to the end wall 111. The negative electrode sheet 123 is coated with a negative electrode active material layer. To improve the energy density of the secondary battery 100, the Si content in the negative electrode active material layer is greater than 2%. However, silicon expands more significantly during lithiation. Considering that the electrode assembly 120 expands cumulatively in the radial direction during charging, the sidewall 112 of the housing 110 plays a key role in restraining the radial expansion of the electrode assembly 120. Therefore, the Vickers hardness of the sidewall 112 is limited to greater than or equal to 160 HV, for example, 160 HV, 165 HV, 170 HV, or 180 HV. A sidewall 112 that meets this hardness requirement can provide better structural support for the electrode assembly 120, thereby protecting the internal components of the battery from external impact and pressure. It can also reduce deformation of the sidewall 112 during battery charging and discharging, better resist internal pressure, and also have high wear resistance. It should be noted that the hardness measurement equipment used is a Vickers hardness tester. The hardness of the sidewall 112 is measured by first measuring the hardness of the sidewall 112 at a position approximately 10 mm from the end wall 111, the middle of the sidewall 112, and the position approximately 5 mm from the opening 113. The hardness values ​​measured at these three locations are then averaged.

[0089] See also Figure 1 and Figure 2In an example of the secondary battery 100 of the present invention, the secondary battery 100 further includes a pole 130. A pole 130 hole is provided on the end wall 111. The pole 130 passes through the pole 130 hole and is insulated and fixed to the end wall 111. The pole 130 is electrically connected to the positive electrode sheet 121. The Vickers hardness of the end wall 111 is greater than 100 HV and less than 150 HV, for example, it can be 100 HV, 110 HV, 120 HV, 130 HV, 140 HV or 150 HV, etc. The Vickers hardness of end wall 111 is greater than the limit of 100 HV, which ensures that end wall 111 has sufficient hardness to provide better structural support. A Vickers hardness of end wall 111 less than the limit of 150 HV makes the hardness of end wall 111 less than that of side wall 112, making it more susceptible to deformation when the internal pressure of the battery is too high. This helps guide pressure release through the terminal 130 and out of the terminal 130 hole at the end wall 111 in the event of failure of other pressure relief structures or other extreme situations, thereby improving battery safety. It should be noted that the hardness measurement equipment used is a Vickers hardness tester, and the hardness of end wall 111 is obtained by measuring the hardness value at 1 / 2 the diameter of end wall 111.

[0090] See also Figure 1 、 Figure 2 and Figure 6 In an example of a secondary battery 100 of the present invention, the housing 110 is electrically connected to the negative electrode plate 123, making the housing 110 a negative output terminal. It can be understood that in the battery pack 10, multiple secondary batteries 100 are connected in series and / or in parallel, and the positive output terminal and the negative output terminal of the secondary battery 100 are welded together via a busbar according to design requirements. Typically, the outer side of the end wall 111 is used for welding to the external busbar. Furthermore, a first nickel plating layer 114 is provided on the outer side of the housing 110. The processing technology of the first nickel plating layer 114 is not limited. For example, it can be formed by nickel plating the outer side of the housing 110 after stretching. Alternatively, a pre-nickel plating method can be used, that is, before the housing 110 is stretched, nickel is first plated on the blank, and then the housing 110 is stretched. After the stretching is completed, the first nickel plating layer 114 extends with the stretching of the housing 110 and adheres to the outer side of the housing 110. The first nickel plating layer 114 not only improves the corrosion resistance, wear resistance and rust resistance of the outer side of the shell 110 , but also improves the welding performance of the shell 110 .

[0091] See also Figure 1 、 Figure 2 and Figure 6, and because the end wall 111 is a welding surface, it is preferred that the thickness of the first nickel plating layer 114 located on the end wall 111 is greater than the thickness of the first nickel plating layer 114 located on the side wall 112, so that the first nickel plating layer 114 located on the end wall 111 has a better soldering effect. In addition, in the battery pack 10, the end wall 111 is in direct contact with the outside world and is often in a complex environment with high temperature and high humidity. Therefore, the end wall 111 has higher requirements for the corrosion resistance, rust resistance and wear resistance of the first nickel plating layer 114. The side wall 112 is wrapped with an insulating film, and in the battery pack 10, the side wall 112 is surrounded by thermal conductive glue or structural glue, so the performance requirements for the first nickel plating layer 114 are relatively low. In addition, since the side wall 112 is a curved surface, the first nickel plating layer 114 on the curved surface has different physical properties from the substrate. If the thickness is too thick, it will be easy to partially peel off when it is worn. Therefore, the thicker thickness of the first nickel plating layer 114 located on the end wall 111 can improve the corrosion resistance, rust resistance and wear resistance of the first nickel plating layer 114, so as to facilitate the end wall 111 to adapt to complex working conditions; the thinner thickness of the first nickel plating layer 114 located on the side wall 112 can reduce costs while meeting the corrosion resistance, rust resistance and wear resistance requirements. In addition, it can also prevent the first nickel plating layer 114 from partially peeling off when worn, resulting in uneven thickness or even local corrosion.

[0092] See also Figure 6 In an example of the secondary battery 100 of the present invention, the thickness of the first nickel-plated layer 114 on the end wall 111 is c, and the thickness of the first nickel-plated layer 114 on the side wall 112 is d, where 1<c / d<3, for example, 1.5, 2, 2.5, 2.9, etc. This further optimizes the corrosion, rust, and wear resistance of the first nickel-plated layer 114. Furthermore, when using a pre-nickel plating process, the stretch ratio of the first nickel-plated layer 114 on the side wall 112 can be limited to a minimum, reducing the possibility of the first nickel-plated layer 114 being broken and preventing pitting corrosion, thereby improving the corrosion and wear resistance of the first nickel-plated layer 114.

[0093] See also Figure 6 It should be noted that the equipment for measuring the thickness of the first nickel-plated layer 114 is a coating thickness gauge. The method for measuring the thickness c of the first nickel-plated layer 114 located on the end wall 111 is as follows: first, the thickness of the first nickel-plated layer 114 is measured at 5 points on the circumference of 1 / 2 diameter of the end wall 111, and then the average value of the 5 values ​​is obtained; the method for measuring the thickness d of the first nickel-plated layer 114 located on the side wall 112 is as follows: first, the thickness of the first nickel-plated layer 114 at 1 / 3 height, 1 / 2 height and 2 / 3 height of the side wall 112 is measured respectively. Specifically, the thickness of the first nickel-plated layer 114 is measured at 5 points on the circumference of each height, and then the average value is obtained to obtain the thickness at each height, and then the average value of the thickness at these three heights is obtained.

[0094] See also Figure 6 In an example of the secondary battery 100 of the present invention, the thickness of the first nickel-plated layer 114 on the end wall 111 ranges from 4 μm to 5 μm, such as 4 μm, 4.2 μm, 4.4 μm, 4.5 μm, 4.8 μm, or 5 μm. The thickness of the first nickel-plated layer 114 on the side wall 112 ranges from 2 μm to 4 μm, such as 2 μm, 2.2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm. Further limiting the thickness ranges of the first nickel-plated layer 114 on the end wall 111 and the first nickel-plated layer 114 on the side wall 112 further optimizes the corrosion, rust, and wear resistance of the first nickel-plated layer 114, and reduces costs while still meeting the corrosion, rust, and wear resistance requirements.

[0095] See also Figure 3 and Figure 6 In one example of a secondary battery 100 according to the present invention, an insulating member 150 is disposed between the end wall 111 and the electrode assembly 120 to isolate the end wall 111 from the electrode assembly 120. The shape and structure of the insulating member 150 are not limited. For example, in some embodiments, the insulating member 150 may be a lower plastic, while in other embodiments, the insulating member 150 may be a bottom support plate, as long as it can provide insulation between the end wall 111 and the positive electrode tab 124 of the electrode assembly 120. To prevent the housing 110 from reacting with the electrolyte or other chemicals within the battery, thereby preventing battery leakage or short circuits due to corrosion and improving battery safety, a second nickel-plated layer 115 is disposed on the inside of the housing 110. There is no limitation on the processing technology of the second nickel plating layer 115. For example, it can be formed by nickel plating on the inner side of the shell 110 after the stretching is completed; or pre-nickel plating can be used, that is, before the shell 110 is stretched, nickel is first plated on the blank, and then the shell 110 is stretched. After the stretching is completed, the first nickel plating layer 114 extends with the stretching of the shell 110 and adheres to the inner side of the shell 110.

[0096] See also Figure 3 and Figure 6Considering the gap between the end wall 111 and the insulating member 150, the electrolyte stored between the end wall 111 and the insulating member 150 is difficult to flow out due to the tension of the liquid, which easily causes liquid-phase corrosion to the inner side of the end wall 111. Therefore, the thickness of the second nickel-plated layer 115 located on the end wall 111 is set to be greater than the thickness of the second nickel-plated layer 115 located on the side wall 112 to overcome the liquid-phase corrosion caused by the residual electrolyte between the end wall 111 and the insulating member 150. In addition, the thinner thickness of the second nickel-plated layer 115 located on the side wall 112 can, on the one hand, reduce costs while meeting the requirements of corrosion resistance, rust resistance, and wear resistance, and on the other hand, reduce the amount of first nickel-plated layer 114 that falls off, thereby improving the corrosion resistance of the second nickel-plated layer 115 and improving the safety performance of the battery.

[0097] See also Figure 6 In an example of the secondary battery 100 of the present invention, the thickness of the second nickel-plated layer 115 on the end wall 111 is e, and the thickness of the second nickel-plated layer 115 on the side wall 112 is f, where 1<e / f<3, for example, 1.5, 2, 2.5, 2.9, etc. This further optimizes the corrosion, rust, and wear resistance of the second nickel-plated layer 115. Furthermore, when using a pre-nickel plating process, the stretch ratio of the second nickel-plated layer 115 on the side wall 112 can be limited to a minimum, reducing the possibility of the second nickel-plated layer 115 being broken and preventing pitting corrosion, thereby improving the corrosion and wear resistance of the first nickel-plated layer 114.

[0098] It should be noted that the equipment for measuring the thickness of the second nickel plating layer 115 is a plating thickness gauge. The method for measuring the thickness e of the second nickel plating layer 115 located on the end wall 111 is as follows: first, take 5 points on the circumference of 1 / 2 diameter of the end wall 111 to measure the thickness of the second nickel plating layer 115 respectively, and then calculate the average value of the 5 values; the method for measuring the thickness f of the second nickel plating layer 115 located on the side wall 112 is as follows: first, measure the thickness of the second nickel plating layer 115 at 1 / 3 height, 1 / 2 height and 2 / 3 height of the side wall 112 respectively. Specifically, first take 5 points on the circumference of each height to measure the thickness of the second nickel plating layer 115 respectively, and then calculate the average value to obtain the thickness at each height, and then calculate the average value of the thickness at these three heights.

[0099] See also Figure 6In an example of the secondary battery 100 of the present invention, the thickness of the second nickel-plated layer 115 on the end wall 111 ranges from 2 μm to 3 μm, such as 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.8 μm, or 3 μm. The thickness of the second nickel-plated layer 115 on the side wall 112 ranges from 1 μm to 2 μm, such as 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.8 μm, or 2 μm. Further limiting the thickness ranges of the second nickel-plated layer 115 on the end wall 111 and the second nickel-plated layer 115 on the side wall 112 further optimizes the corrosion resistance of the second nickel-plated layer 115 and reduces costs while maintaining corrosion resistance.

[0100] See also Figure 6 In one example of the secondary battery 100 of the present invention, the thickness of the first nickel-plated layer 114 is greater than the thickness of the second nickel-plated layer 115 along the same thickness direction of the housing 110. The thicker first nickel-plated layer 114 on the outside of the housing 110 improves the wear resistance, corrosion resistance, and rust resistance of the outside of the housing 110, enabling the housing 110 to adapt to complex external operating environments. The thinner second nickel-plated layer 115 on the inside of the housing 110 reduces the risk of nickel shedding. Since metal powder remaining inside the battery may cause micro-short circuits and increase the risk of thermal runaway, this configuration can improve the safety performance of the battery while also providing corrosion resistance to the inside of the housing 110.

[0101] See also Figure 3 When the shell 110 is stamped and stretched, the sudden change in size can easily lead to stress concentration, reduced elongation at break, and reduced structural strength. This is especially true at the junction of the end wall 111 and the side wall 112, which is both a corner and has a change in wall thickness. Therefore, in an example of the secondary battery 100 of the present invention, please refer to Figure 3The end wall 111 and the side wall 112 are connected by a transition portion 116. The transition portion 116 includes a first fillet 1161 connecting the outer surface of the end wall 111 and the outer surface of the side wall 112, and a second fillet 1162 connecting the inner surface of the end wall 111 and the inner surface of the side wall 112. The radius of the first fillet 1161 is r1, and the radius of the second fillet 1162 is r2. The ratio of the radius r1 of the first fillet 1161 to the wall thickness of the end wall 111 is limited to r1 / a≥1, for example, it can be: 1, 1.5, 2, 2.5, 3 or 4, etc.; the radius r2 of the second fillet 1162 is limited to the range of r2 / a≥1, for example, it can be: 1, 1.5, 2, 2.5, 3 or 4, etc. It should be noted that the radius r1 of the first fillet 1161 and the radius r2 of the second fillet 1162 are measured using a profilometer. The measurement method involves scanning the entire arc surface with the profilometer and taking the radius that coincides with the arc surface as the measured fillet radius. This dimension restriction ensures a smooth transition from the end wall 111 to the side wall 112. This prevents tensile fracture caused by a sharp transition and, when using a pre-nickel plating process, reduces nickel plating shedding during the stretching of the side wall 112. Furthermore, it alleviates stress concentration at the corner between the end wall 111 and the side wall 112.

[0102] In an example of the secondary battery 100 of the present invention, please refer to Figure 3 The ratio of the wall thickness formed by the first fillet 1161 and the second fillet 1162 of the transition portion 116 to the thickness of the end wall 111 is further limited to: 0.8≤(r1-r2) / a≤0.95, and can be, for example, 0.8, 0.85, 0.9, or 0.95. This ratio is limited to this range to achieve a gradual transition between the end wall 111 and the transition portion 116. This prevents tensile fracture caused by a sharp transition and, when a pre-nickel plating process is used, reduces the loss of the nickel plating during the stretching of the side wall 112.

[0103] In an example of the secondary battery 100 of the present invention, please refer to Figure 3The transition portion 116 is gradually stretched from the inner surface of the end wall 111 facing the interior of the shell 110 along the axial direction of the side wall 112 to be equal to the wall thickness of the side wall 112. The stretched height of the transition portion 116 is h, 0.5≤r1 / h≤1, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1. The ratio of the radius of the first fillet 1161 to the stretched height is limited to 0.5≤r1 / h≤1. r1 / h≥0.5 can achieve a smooth transition from the end wall 111 to the side wall 112. On the one hand, it can prevent tensile fracture caused by a sharp transition. On the other hand, when using a pre-nickel plating process, it can also reduce the shedding of the nickel plating during the stretching process of the side wall 112. On the other hand, it can also alleviate stress concentration at the corner of the end wall 111 and the side wall 112. The limitation of R1 / h≤1 can prevent the internal components of the battery from interfering with the transition portion 116 when entering the shell.

[0104] Preferably, in an example of the secondary battery 100 of the present invention, please refer to Figure 3 The radius r1 of the first fillet 1161 is further limited to: 1mm≤r1≤1.5mm, and the stretched height is limited to: 1mm≤h≤2mm. This configuration not only achieves a smooth transition from the end wall 111 to the side wall 112, but also prevents interference between the internal battery components and the transition portion 116 when the battery is inserted into the shell.

[0105] In an example of the secondary battery 100 of the present invention, please refer to Figure 3 and Figure 5 Along the axial direction of the electrode assembly 120, the electrode assembly 120 includes a reaction zone 127 and two non-reactive zones 128 located on either side of the reaction zone 127. The reaction zone 127 is the radially overlapping portion of the first coating zone 1212 and the second coating zone 1232 of the electrode assembly 120. During the battery charge and discharge process, because the first coating zone 1212 and the second coating zone 1232 of the reaction zone 127 of the electrode assembly 120 overlap in the radial direction of the electrode assembly 120, the reaction zone 127 expands cumulatively in the radial direction, resulting in a significant expansion force that exerts significant pressure on the sidewall 112. The non-reactive zone 128 is the portion consisting of only the first coating zone 1212 or only the second coating zone 1232. It can be understood that the non-reactive zone 128 on the positive electrode tab 124 side is the portion consisting of only the first coating zone 1212, and the non-reactive zone 128 on the negative electrode tab 125 side is the portion consisting of only the second coating zone 1232.

[0106] Further, see Figure 3 and Figure 5The distance from the boundary between a non-reactive zone 128 and a reactive zone 127 near the end wall 111 to the inner side of the end wall 111 is defined as g, and g ≥ h. That is, the distance from the boundary between the non-reactive zone 128 and the reactive zone 127 to the inner side of the end wall 111 is defined as greater than the stretched height of the transition portion 116. It should be noted that when the positive electrode tab 124 is near the end wall 111, the non-reactive zone 128 near the end wall 111 is comprised of only the first coating zone 1212. When the negative electrode tab 125 is near the end wall 111, the non-reactive zone 128 near the end wall 111 is comprised of only the second coating zone 1232. In this embodiment, the positive electrode tab 124 is near the end wall 111, and the non-reactive zone 128 near the end wall 111 contains only positive electrode active material and no negative electrode active material. Therefore, lithium ions do not migrate in the non-reactive zone 128, and the non-reactive zone 128 does not expand. Therefore, the limitation of g≥h can ensure that the reaction zone 127 does not overlap with the transition portion 116. Even if the reaction zone 127 is located at a portion where the wall thickness of the side wall 112 is relatively uniform, it can prevent the reaction zone 127 from pressing against the transition portion 116 first during expansion, causing the shell 110 to break at the transition portion 116. At the same time, it can ensure that the pressure applied to the side wall 112 during expansion of the electrode assembly 120 is uniform, thereby improving the safety performance of the battery.

[0107] See also Figure 7 The present invention further provides a battery pack 10, comprising any of the aforementioned secondary batteries 100. In one embodiment of the battery pack 10 of the present invention, the battery pack 10 comprises a housing 101, a housing cover 102, and a plurality of secondary batteries 100. The plurality of secondary batteries 100 are placed within the housing 101 and connected in series or in parallel, or in a combination of these. The housing cover 102 seals the housing 101 to protect the plurality of secondary batteries 100. It should be noted that, in addition to the secondary batteries 100 of the present invention, the battery pack 10 may also include a thermal management system, a circuit board, and other components. The battery pack 10 may be a battery module, a battery pack, an energy storage cabinet, or the like; these will not be described in detail here.

[0108] See also Figure 8The present invention also provides an electronic device 1, which includes the above-mentioned battery pack 10. The working part 11 is electrically connected to the battery pack 10 to obtain power support. As an example, the electronic device 1 is a vehicle, and the vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc., but is not limited to this. The working part 11 is the vehicle body, and the battery pack 10 is arranged at the bottom of the vehicle body and provides power support for the driving of the vehicle or the operation of the electrical components in the vehicle. However, in some other embodiments, the electronic device 1 can also be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy and an electric tool, etc. Spacecraft include airplanes, rockets, space shuttles and spacecraft, etc.; the working part 11 can be a unit component that can obtain power from the battery pack 10 and perform corresponding work, such as a fan blade rotation unit, a vacuum cleaner's dust collection unit, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys; electric tools include metal cutting tools, grinding tools, assembly tools, and railway tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. The present embodiment does not impose any particular restrictions on the electronic device 1.

[0109] In the secondary battery of the present invention, the end walls are not stretched or stretched to a very small extent, so the wall thickness of the end walls is approximately equal to the thickness of the raw material. By limiting the ratio between the end wall thickness and the side wall thickness to within the range of 1 < a / b < 3, the radial dimension of the shell perpendicular to the stretching direction along the height direction of the shell does not fluctuate excessively during the gradual thinning process of multiple stretching, which is beneficial to the consistency of the finished shell. In addition, the shell exerts a relatively uniform pressure on the side of the electrode assembly, thereby optimizing the performance of the secondary battery. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and practical significance. The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A secondary battery, characterized in that: include: The shell comprises an end wall and a side wall surrounding the end wall, wherein the side wall and the end wall are integrally formed by stretching; an electrode assembly, housed in the housing; The thickness of the end wall is a, the thickness of the side wall is b, and 1<a / b<3.

2. The secondary battery according to claim 1, wherein 1.3≤a / b≤2.

3. The secondary battery according to claim 1, wherein The secondary battery is a cylindrical battery, the diameter of the end wall is D, the height of the side wall is L, and 1.5≤L / D≤3.

5.

4. The secondary battery according to claim 3, wherein The range of the diameter of the end wall is: 30mm≤D≤50mm.

5. The secondary battery according to claim 1, wherein The secondary battery is a cylindrical battery, and the tolerance of the diameter of the shell is less than or equal to 0.07 mm.

6. The secondary battery according to claim 1, wherein The secondary battery is a cylindrical battery, and the roundness of the shell is less than or equal to 0.09 mm.

7. The secondary battery according to claim 1, wherein The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator stacked and wound to form a wound body, the winding axis of the wound body is perpendicular to the end wall, the negative electrode sheet is coated with a negative electrode active material layer, the Si content in the negative electrode active material layer is greater than 2%, and the Vickers hardness of the side wall is greater than or equal to 160HV.

8. The secondary battery according to claim 7, wherein: The secondary battery also includes a pole, a pole hole is provided on the end wall, the pole passes through the pole hole and is insulated and fixed to the end wall, the pole is electrically connected to the positive electrode plate, and the Vickers hardness of the end wall is greater than 100HV and less than 150HV.

9. The secondary battery according to claim 8, wherein The shell is electrically connected to the negative electrode plate, the outer side of the end wall is used for welding to the external bus bar, and the outer side of the shell is provided with a first nickel plating layer, and the thickness of the first nickel plating layer located on the end wall is greater than the thickness of the first nickel plating layer located on the side wall.

10. The secondary battery according to claim 9, wherein The thickness of the first nickel plating layer located on the end wall is c, and the thickness of the first nickel plating layer located on the side wall is d, wherein 1<c / d<3.

11. The secondary battery according to claim 10, wherein The thickness of the first nickel plating layer located on the end wall is in a range of 4 μm to 5 μm, and the thickness of the first nickel plating layer located on the side wall is in a range of 2 μm to 4 μm.

12. The secondary battery according to claim 9, wherein An insulating member is provided between the end wall and the electrode assembly to isolate the end wall and the electrode assembly, a second nickel plating layer is provided on the inner side of the shell, and the thickness of the second nickel plating layer located on the end wall is greater than the thickness of the second nickel plating layer located on the side wall.

13. The secondary battery according to claim 12, characterized in that The thickness of the second nickel plating layer located on the end wall is e, and the thickness of the second nickel plating layer located on the side wall is f, wherein 1<e / f<3.

14. The secondary battery according to claim 13, wherein: The thickness of the second nickel plating layer located on the end wall is in the range of 2 μm to 3 μm, and the thickness of the second nickel plating layer located on the side wall is in the range of 1 μm to 2 μm.

15. The secondary battery according to claim 12, wherein: Along the same thickness direction of the shell, the thickness of the first nickel plating layer is greater than the thickness of the second nickel plating layer.

16. The secondary battery according to claim 1, wherein The end wall and the side wall are connected by a transition portion, and the transition portion includes a first rounded corner connecting the outer surface of the end wall and the outer surface of the side wall and a second rounded corner connecting the inner surface of the end wall and the inner surface of the side wall, the radius of the first rounded corner is r1, and the radius of the second rounded corner is r2, wherein r1 / a≥1, r2 / a≥1.

17. The secondary battery according to claim 16, wherein: 0.8≤(r1-r2) / a≤0.95。 18. The secondary battery according to claim 16, wherein The transition portion is gradually stretched along the axial direction of the side wall from the inner surface of the end wall facing the interior of the shell to be equal to the wall thickness of the side wall. The stretching height of the transition portion is h, wherein 0.5≤r1 / h≤1.

19. The secondary battery according to claim 18, wherein 1mm≤r1≤1.5mm, 1mm≤h≤2mm.

20. The secondary battery according to claim 18, wherein The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a winding body formed by stacking and winding a separator. The positive electrode sheet includes a first coating area coated with a positive electrode active material and a first uncoated area not coated with the positive electrode active material. The negative electrode sheet includes a second coating area coated with a negative electrode active material and a second uncoated area not coated with the negative electrode active material. Along the axial direction of the electrode assembly, the electrode assembly includes a reaction area and two non-reaction areas respectively located on both sides of the reaction area. The reaction area is the part where the first coating area and the second coating area overlap along the radial direction of the electrode assembly. The non-reaction area is the part where only the first coating area or only the second coating area is present. The distance from the boundary line between the non-reaction area and the reaction area close to the end wall to the inner side of the end wall is g, where g≥h.

21. The secondary battery according to claim 1, wherein The shell is a steel shell.

22. The secondary battery according to claim 1, wherein The side wall has an opening at one end away from the end wall, and the side wall close to the opening includes a rolling groove recessed toward the interior of the shell, the rolling groove forms a bulge inside the side wall, and the open end of the side wall is bent toward the center of the shell to form a flange; the secondary battery also includes an end cover, which is sealed and installed between the bulge and the flange.

23. A battery pack, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 22.

24. An electronic device, characterized in that: A battery pack comprising the battery pack of claim 23.

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