Secondary battery and electronic device

Abstract

The utility model provides a secondary battery and an electronic device, the secondary battery comprises a shell, the shell comprises an end wall and a side wall surrounding the end wall, the side wall and the end wall are integrally stretched and formed, an opening is formed in one end, deviating from the end wall, of the side wall, N stretching lines surrounding the periphery of the side wall are arranged on the side wall along the height direction of the side wall, and N is a natural number greater than 2; in the direction from the end wall to the opening, the distance from the first stretching line to the outer surface of the end wall is S1, the distance from the second stretching line to the first stretching line is S2, and so on, the distance from the Nth stretching line to the (N-1) th stretching line is SN, S1 < S2 <... < SN, and the single discharging amount in the shell stretching process is optimized, so that the product yield of the battery shell is increased.

Description

TECHNICAL FIELD

[0001] The utility model relates to a battery technical field, concretely relates to a secondary battery and electronic device. BACKGROUND

[0002] Stretching process is a kind of stamping processing method that metal plate is stretched into the shape required by die, has the advantages such as high production efficiency, high material utilization and can adapt to complex shape, is commonly applied to the processing of the shell of battery.For the shell of battery, stretching process can make metal plate form cylindrical, square or polygonal shell with certain thickness and shape.

[0003] The processing of shell needs to be completed by the stretching of plate material for many times, and in the shell stretching process, the radial dimension of the cavity gradually becomes smaller, and every time the steel plate contacts the cavity, the material on the steel plate will be turned up, and the gradually high and thin sidewall is formed by multiple stretching.The risk of steel shell cracking exists when the single discharge amount is too large, and the single discharge amount is too small, which increases the stretching frequency, increases the cost, and also causes the risk of appearance defect and size fluctuation, thereby reducing the product yield.So, optimizing the single discharge amount is an important technical difficulty in shell processing. SUMMARY

[0004] The utility model provides a kind of secondary battery and electronic device, by the optimization of single discharge amount in the shell stretching process, to improve the product yield of battery shell.

[0005] To achieve the above object and other related purposes, the utility model provides a kind of secondary battery and electronic device, the secondary battery includes shell, including end wall and the sidewall around end wall, sidewall and end wall are integrally stretched and formed, the opening is formed in the end of sidewall away from end wall, along the height direction of sidewall, N stretch lines around the outer periphery of sidewall are arranged on sidewall, N is the natural number greater than 2;Along the direction of end wall to opening, the distance between first stretch line and the outer surface of end wall is S1, the distance between second stretch line and first stretch line is S2, by analogy, the distance between N stretch line and N-1 stretch line is SN, S1<S2<……<SN.

[0006] In the technical scheme, during the stretching of the shell, the radial size of the cavity gradually decreases, and each time the steel plate contacts the cavity, the material on the steel plate is turned up and stretched to form a thinner side wall, and a stretch mark is left on the outer surface of the steel plate. As the stretching proceeds, the stretch marks formed each time are sequentially arranged on the outer periphery of the side wall. In the direction from the end wall to the opening, N stretch marks are sequentially defined as a first stretch mark, a second stretch mark, and an Nth stretch mark. The distance between the first stretch mark and the end wall is S1, the distance between the second stretch mark and the first stretch mark is S2, and the distance between the Nth stretch mark and the (N-1)th stretch mark is SN. Therefore, the portions of the side wall corresponding to the S1 distance section, the S2 distance section, and the SN distance section are all related to the discharge amount of each time. Since the wall thickness of the side wall is uniform except for the S1 distance section, the S1 distance section is less than the S2 distance section, and the SN distance section is less than the (N-1)th stretch mark, the discharge amount of each time is less than that of the previous time, that is, the single discharge amount gradually decreases during the entire stretching process of the shell. This arrangement can reduce the risk of cracking of the steel shell.

[0007] Specifically, since the S1 distance section needs to be stretched once, the SN-1 distance section needs to be stretched N-1 times, and the SN distance section needs to be stretched N times, that is, in the direction from the end wall to the opening, the number of stretchings required for each section increases sequentially. Therefore, the arrangement of S1 < S2 < … < SN can ensure that the SN distance section has sufficient material to maintain the same wall thickness after N stretchings, and the SN-1 distance section has sufficient material to maintain the same wall thickness after N-1 stretchings. Thus, the thickness of each section is reduced from the original thickness of the plate to the target thickness of the side wall, thereby improving the appearance and size fluctuation of the side wall, improving the size accuracy and structural strength of the side wall, and improving the yield of the shell.

[0008] In the example of the secondary battery of the present application, 4 ≤ N ≤ 14.

[0009] In the technical scheme, since one stretch mark corresponds to one stretching, the limitation of 4 ≤ N ≤ 14 means that the shell is stretched 4-14 times. N ≥ 4 can ensure that the discharge amount of each time is not too high, thereby reducing the risk of cracking of the shell. Since the breaking elongation rate decreases with each stretching of the side wall, N ≤ 14 can ensure that the number of stretchings of the shell is not too high, thereby preventing the side wall from being pulled apart due to the decrease in breaking elongation rate, and also achieving the beneficial effects of reducing the number of steps, reducing costs, and improving the appearance.

[0010] In the example of the secondary battery of the present application, the thickness of the side wall is H, the circumference of the side wall is L, and LxHxSN ≤ 2000mm 3 .

[0011] In the technical scheme, LxHxSN ≤ 2000mm 3The volume of the part between each adjacent stretch line is less than or equal to 2000mm 3 The volume of the part between each adjacent stretch line is less than or equal to 2000mm 3 The volume of the part between each adjacent stretch line is less than or equal to 2000mm

[0012] In the secondary battery example of the utility model, the side wall comprises a variable wall thickness area and a uniform wall thickness area, the variable wall thickness area is located in the part between the first stretch line and the end wall, the variable wall thickness area connects the end wall and the uniform wall thickness area, the variable wall thickness area comprises a thick wall end connected with the end wall and a thin wall end connected with the uniform wall thickness area, and the wall thickness of the thin wall end is equal to the thickness of the uniform wall thickness area.

[0013] In the above technical solution, the variable wall thickness area is arranged at the connection between the end wall and the side wall, so that smooth transition from the end wall to the side wall can be realized, which can prevent stretch fracture caused by sharp transition and is beneficial to the release of internal stress and the improvement of the strength and service life of the shell.

[0014] In the secondary battery example of the utility model, the secondary battery further comprises an electrode assembly accommodated in the shell, the electrode assembly comprises a winding body formed by laminating and winding a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet comprises a first coating area coated with a positive active material and a first uncoated area without the positive active material, the negative electrode sheet comprises a second coating area coated with a negative active material and a second uncoated area without the negative active material, along the axial direction of the electrode assembly, the electrode assembly comprises a reaction area and two non-reaction areas located on both sides of the reaction area, the reaction area is the part in which the first coating area and the second coating area coincide in the radial direction of the electrode assembly, the non-reaction area is the part with only the first coating area or only the second coating area, and 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 A, and the distance from the thin wall end to the inner side of the end wall is B, A is greater than or equal to B.

[0015] In the above technical solution, in the process of charging and discharging of the battery, since the first coating area and the second coating area in the reaction area of the electrode assembly coincide in the radial direction of the electrode assembly, the reaction area expands in the radial direction, the expansion force is large, and a large pressure is applied to the side wall, while the non-reaction area of the electrode assembly has only the first coating area or only the second coating area, and does not expand, so that the distance from the boundary line between the non-reaction area and the reaction area to the inner side of the end wall is greater than or equal to the distance from the thin wall end to the inner side of the end wall, the reaction area does not coincide with the variable wall thickness area, but coincides with the uniform wall thickness area of the side wall, which can prevent the reaction area from pressing the variable wall thickness area first when expanding and causing the shell to break at the variable wall thickness area, and can also realize that the pressure applied to the side wall by the electrode assembly when expanding is uniform, thereby improving the safety performance of the battery.

[0016] In the secondary battery example of the utility model, the thickness of the uniform wall thickness area is T1, the thickness of the end wall is T2, and T2 / T1≤3.

[0017] In the above technical solution, the end wall is not stretched or is stretched to a small degree, so the thickness T2 of the end wall is approximately equal to the thickness of the plate material, the part between the first stretching line and the end wall is the last time of stretching forming and is one-time stretching forming, by limiting the ratio between the thickness of the end wall and the thickness of the side wall within the range of T2 / T1≤3, the stretching ratio of the last time of stretching of the S1 distance section can be controlled to be not too large, so as to reduce the probability of fracture of the S1 distance section during the last time of stretching.

[0018] In the secondary battery example of the utility model, the secondary battery is a cylindrical battery, the cylindrical battery further includes an electrode assembly accommodated in the shell, the inner diameter of the shell is D1, the electrode assembly includes a center hole, the diameter of the center hole is D2, when D2 / D1≤0.18, T2 / T1≥2.

[0019] In the above technical solution, the limitation of D2 / D1≤0.18 makes the battery have a larger battery capacity, but the smaller the diameter D2 of the center hole is, the greater the pressure of the electrode assembly on the shell is when the electrode assembly expands, further limiting T2 / T1≥2 means that the shell needs to be stretched multiple times, since the stretching process has a work hardening effect, each stretching is beneficial to improving the hardness of the side wall, realizing that the side wall can withstand greater pressure without being prone to fracture, and further improving the comprehensive performance of the battery.

[0020] In the secondary battery example of the utility model, the circumferential fracture elongation rate of the side wall is less than or equal to 5%.

[0021] In the above technical solution, the circumferential fracture elongation rate of the side wall is further limited to be less than or equal to 5%, which can realize the effect that the side wall is not prone to deformation when the internal pressure increases, so that the battery maintains a stable outer dimension, and the battery is convenient for assembly in a battery module.

[0022] In the secondary battery example of the utility model, the shell material is steel.

[0023] In the above technical solution, the steel shell has excellent properties of wear resistance, corrosion resistance, dust prevention and water resistance, and can achieve better protection performance.

[0024] The utility model also provides an electronic device, including battery group, battery group includes the secondary battery of any one of the above.

[0025] The utility model discloses secondary battery, in the shell stretching process, because the radial dimension of cavity gradually becomes small, every time when the steel sheet and cavity contact, the material on the steel sheet will be turned up and form the thin side wall through stretching, and leave the stretch mark on the outer surface of the steel sheet and cavity contact, along the direction of end wall to opening, N stretch marks are defined as first stretch mark, second stretch mark... N stretch mark in proper order, the distance between first stretch mark and end wall is S1, the distance between second stretch mark and first stretch mark is S2, and so on, the distance between N stretch mark and N-1 stretch mark is SN. Then the part of S1 section, S2 section... SN section on the side wall should be in proper order with the discharge capacity, and because the side wall is equal wall thickness except S1 section, therefore, limit S1 < S2 <... < SN, can realize the discharge capacity of every time is less than the discharge capacity of last time, namely the single discharge capacity gradually decreases in the whole stretching process of shell, and this setting can reduce the risk of steel shell cracking.

[0026] Specifically, because S1 section needs to pass through once stretching, SN-1 section needs to pass through N-1 times stretching, and SN section needs to pass through N times stretching, namely along the direction of end wall to opening, the number of stretching times that each section needs to pass through increases in proper order, therefore, the setting of S1 < S2 <... < SN can make that SN section has sufficient material to maintain the same wall thickness with other distance sections after N times stretching, and also make that SN-1 section has sufficient material to pass through N-1 times stretching, so as to realize that the thickness of each section is thinned from the original thickness of plate material to the target thickness of side wall, and then improve the problem of side wall appearance bad and size fluctuation, be favorable to improving the size precision and structural strength of side wall, and then improve the yield of shell. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical scheme in the embodiments of the utility model or prior art, the following will briefly introduce the drawings needed to be used in embodiment or prior art description, and obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other embodiments can also be obtained according to these drawings without creating creative labor.

[0028] Figure 1 It is the structural schematic diagram of secondary battery one embodiment of the utility model;

[0029] Figure 2 It is the structural schematic diagram of electrode assembly one embodiment of the utility model;

[0030] Figure 3 It is Figure 1 The local enlarged view of A in middle;

[0031] Figure 4Structure diagram of the shell of the secondary battery according to an embodiment of the present application;

[0032] Figure 5 Structure diagram of the square shell battery according to an embodiment of the secondary battery of the present application;

[0033] Figure 6 Sectional view of the square shell battery according to an embodiment of the secondary battery of the present application;

[0034] Figure 7 Structure diagram of the battery pack according to an embodiment of the electronic device of the present application;

[0035] Figure 8 Structure diagram of an embodiment of the electronic device of the present application.

[0036] Element number explanation

[0037] 1, electronic device; 10, battery pack; 11, working part; 101, box body; 102, box cover; 100, secondary battery; 110, shell; 111, end wall; 112, side wall; 1121, variable wall thickness area; 11211, thick wall end; 11212, thin wall end; 1122, uniform wall thickness area; 113, opening; 114, transition fillet; 115, stretch mark; 120, electrode assembly; 121, positive plate; 1211, positive current collector; 1212, first coating area; 1213, first non-coating area; 122, separator; 123, negative plate; 1231, negative current collector; 1232, second coating area; 1233, second non-coating area; 124, positive tab; 125, negative tab; 126, winding body; 127, reaction area; 128, non-reaction area; 130, pole; 140, end cover. DETAILED DESCRIPTION

[0038] The embodiments of the present application will be described in detail with specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. The present application can also be implemented or applied in different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. It should also be understood that the terms used in the embodiments of the present application are for describing specific specific embodiments, and are not intended to limit the protection scope of the present application. The test methods in the following embodiments are not specified, and are usually performed according to conventional conditions or according to the conditions recommended by the manufacturers.

[0039] When the embodiments give a numerical range, it should be understood that, unless otherwise stated by the utility model, both ends of each numerical range and any number between the two ends can be selected. Unless otherwise defined, all technical and scientific terms used in the utility model are used in the same meaning as understood by those skilled in the present art and the description of the utility model, and any method, equipment and material of the prior art similar or equivalent to the method, equipment and material in the embodiments of the utility model can be used to realize the utility model.

[0040] It should be understood that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in the specification are only for the convenience of clear description, and are not intended to limit the scope of the utility model, and the change or adjustment of the relative relationship is also regarded as the scope of the utility model without substantial change of the technical content.

[0041] The secondary battery includes an electrode assembly, which is a component in which an electrochemical reaction occurs in the secondary battery, and can include one or more electrode assemblies.

[0042] The secondary battery further includes a case, an end cover and a pole, the case includes an end wall and a side wall surrounding the end wall, the end wall and the side wall are integrally stretch formed, one end of the side wall has an opening, the electrode assembly can be assembled into the case through the opening of the case, the end cover is used to cover the opening of the case to achieve sealing, and the pole is electrically connected with the electrode assembly through the end wall to guide the electric energy generated by the electrode assembly out.

[0043] In some embodiments, the processing of the case of the battery adopts a stretching process. For the case of the battery, the stretching process can make the metal plate form a cylindrical, square or polygonal case with a certain thickness and shape.

[0044] However, the inventors found that, in the stretching process of the case, since the radial size of the cavity gradually decreases, each time the steel plate is in contact with the cavity, the material on the steel plate will be turned up, and the gradually high and thin side wall is formed through multiple stretching. If the material output of each time is too large, there is a risk of cracking of the steel shell, and if the material output of each time is too small, the number of stretching is increased, the cost is increased, and there is a risk of poor appearance and size fluctuation, thereby reducing the yield of the product. Therefore, optimizing the material output of each time is an important technical difficulty in the processing of the case.

[0045] In view of this, the utility model provides a technical scheme, which limits S1

[0046] Please refer toFigures 1 to 8 The utility model provides a kind of secondary battery 100 and electronic device 1, the secondary battery 100 includes shell 110, electrode assembly 120, pole 130 and end cap 140.

[0047] Please refer to Figure 1 And Figure 2 Shell 110 includes end wall 111 and the side wall 112 around end wall 111, side wall 112 and end wall 111 are integrally stretch-formed, and stretch process is a kind of stamping processing method to be stretched into the shape required by die to metal sheet, specifically, in the embodiment, first, suitable die is selected according to the target shape of shell 110, for example, the shape of shell 110 can be square shell, cylindrical shell or polygonal prism shell etc., then blank is stamped, and the first step is to stamp out the rudiment of end wall 111, side wall 112 and cavity, to ensure the reliability of stretching, avoid stretching fracture, it also needs to be replaced with different size die multiple times and stamp multiple times until stretching to preset size.

[0048] In some embodiments, the shape of shell 110 can be square shell, please refer to Figure 5 And Figure 6 In the embodiment, please refer to Figure 1 The outer edge of end wall 111 is circular, and side wall 112 is in the form of a cylinder and surrounds the outer edge of end wall 111, and a circular opening 113 is formed at one end of side wall 112 away from end wall 111. The shell 110 surrounded by the end wall 111 and the side wall 112 forms a receiving cavity for accommodating the electrode assembly 120, the electrolyte and other necessary components of the battery. Specifically, the diameter of the shell 110 can be determined according to the size of the electrode assembly 120, such as 18mm, 21mm, 46mm, etc. The material of the shell 110 can be various, such as copper, iron, aluminum, steel, aluminum alloy, etc. In order to prevent rusting of the shell 110 during long-term use, a layer of anti-rust material such as metal nickel can be plated on the surface of the shell 110.

[0049] During the stretching of the shell 110, as the radial dimension of the cavity gradually decreases, each time the steel plate contacts the cavity, material on the steel plate is turned up and a thinner side wall 112 is formed by stretching, while leaving stretch marks 115 on the outer surface of the steel plate in contact with the cavity. As the stretching proceeds, each time the stretch marks 115 formed are finally arranged in turn on the outer periphery of the side wall 112. In this embodiment, along the height direction of the side wall 112, the side wall 112 is arranged with N stretch marks 115 around the outer periphery of the side wall 112, N being a natural number greater than 2; along the direction from the end wall 111 to the opening 113, the N stretch marks 115 are defined in turn as the first stretch mark 115, the second stretch mark 115, …, the Nth stretch mark 115; further, the distance from the first stretch mark 115 to the outer surface of the end wall 111 is S1, the distance between the first stretch mark 115 and the second stretch mark 115 is S2, and so on, the distance between the Nth stretch mark 115 and the (N-1)th stretch mark 115 is SN. Then the portions of the side wall 112 in the S1 distance section, the S2 distance section, …, the SN distance section are all proportional to the discharge amount of each time, and since the side wall 112 is of equal thickness except for the S1 distance section.

[0050] Further, S1 < S2 < … < SN is defined, which can achieve that the discharge amount of each time is less than the discharge amount of the last time, i.e. the single discharge amount gradually decreases during the entire stretching process of the shell 110, which can reduce the risk of cracking of the steel shell. In addition, since the S1 distance section needs to be stretched once, the SN-1 distance section needs to be stretched N-1 times, and the SN distance section needs to be stretched N times, i.e. the number of stretching times required for each section increases in turn along the direction from the end wall 111 to the opening 113, so the setting of S1 < S2 < … < SN can make the SN section have sufficient material to maintain the same wall thickness as other distance sections after N times of stretching, and also make the SN-1 distance section have sufficient material to achieve the thickness of each section from the original thickness of the plate to the target thickness of the side wall 112, thereby improving the problem of poor appearance and size fluctuation of the side wall 112, which is beneficial to improve the size precision and structural strength of the side wall 112, and thereby improve the yield of the shell 110. In this embodiment, please refer to Figure 4 , N is equal to 6, i.e. the surface of the shell 110 has 6 stretch marks 115. It should be noted that the actual stretch marks 115 are not absolutely straight lines, and the lines shown in the figure are only for illustration. The distance between each two adjacent stretch marks 115 is measured by drawing a straight line along the height direction of the secondary battery 100 on the side wall 112, and each stretch mark 115 intersects with the above-mentioned straight line auxiliary line, and the distance between adjacent intersection points is regarded as the distance between adjacent stretch marks 115.

[0051] Please refer to Figures 1 to 3The electrode assembly 120 is accommodated in the case 110, and is a component in which an electrochemical reaction occurs in the lithium ion secondary battery 100. One or more electrode assemblies 120 can be included in the case 110. The electrode assembly 120 includes a positive electrode tab 121, a negative electrode tab 123, and a separator 122, which are stacked and wound to form a wound body 126. Specifically, the positive electrode tab 121 includes a positive electrode current collector 1211 and a positive electrode active material coated on a surface of the positive electrode current collector 1211; the positive electrode current collector 1211 includes a first coated region 1212 coated with the active material and a first uncoated region 1213 not coated with the active material, the first uncoated region 1213 being located at an end of the positive electrode tab 121, the first uncoated region 1213 extending beyond the separator 122 in a direction of a winding axis of the electrode assembly 120 and being bent toward the winding axis to form a positive electrode tab 124. The negative electrode tab 123 includes a negative electrode current collector 1231 and a negative electrode active material coated on a surface of the negative electrode current collector 1231; the negative electrode current collector 1231 includes a second coated region 1232 coated with the active material and a second uncoated region 1233 not coated with the active material, the second uncoated region 1233 being located at an end of the negative electrode tab 123, the second uncoated region 1233 extending beyond the separator 122 in the direction of the winding axis of the electrode assembly 120 and being bent toward the winding axis to form a negative electrode tab 125.

[0052] Referring to Figures 1 to 3 The separator 122 is disposed between the positive electrode tab 121 and the negative electrode tab 123 to separate the positive electrode active material layer and the negative electrode active material layer. In the case of the lithium ion secondary battery 100, the positive electrode current collector 1211 can be made of aluminum, the positive electrode active material layer can include a positive electrode active material, and the positive electrode active material can be lithium cobaltate, lithium iron phosphate, ternary lithium, or lithium manganate. The negative electrode current collector 1231 can be made of copper, the negative electrode active material layer can include a negative electrode active material, and the negative electrode active material 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 be coated on the outside of the electrode assembly 120, and the insulating film can be made of PP, PE, polyethylene terephthalate (PET), polyvinyl chloride (PVC), or other high-molecular polymer materials.

[0053] Referring to Figures 1 to 3Further, the positive tab 124 faces the end wall 111 or the opening 113, and the negative tab 125 faces the other end of the shell 110. In this embodiment, the positive tab 124 faces the end wall 111, and the pole 130 is electrically connected to the positive tab 124 to make the pole 130 positively charged. The negative tab 125 faces the opening 113, and the shell 110 is electrically connected to the negative tab 125 to make the shell 110 negatively charged. However, in another embodiment, the negative tab 125 can be connected to the pole 130, and the positive tab 124 can be connected to the shell 110.

[0054] Referring to Figure 1 In this embodiment, the secondary battery 100 further includes a pole 130. Specifically, the pole 130 penetrates the end wall 111 and is insulated from the end wall 111. The pole 130 is directly or indirectly electrically connected to the positive tab 124 through the end wall 111 toward one end of the electrode assembly 120. The pole 130 can have any suitable form that can electrically connect to the positive tab 124 of the electrode assembly 120 through the end wall 111, such as a circular, square, prismatic, or any other suitable cross-sectional shape that can achieve stable electrical conduction. In this embodiment, the pole 130 has a circular cross-section.

[0055] Referring to Figure 1 In this embodiment, the secondary battery 100 further includes an end cover 140. The end cover 140 is sealingly installed in the opening 113. The outer edge of the end cover 140 has a shape corresponding to that of the opening 113 and is connected to the side wall 112 to seal the opening 113.

[0056] Referring to Figure 4 In one example of the secondary battery 100 of the present application, 4≤N≤14. Since each contact between the steel plate and the mold cavity leaves a stretch mark 115 on the outer surface of the steel plate in contact with the mold cavity, one stretch mark 115 corresponds to one stretch. The limitation of 4≤N≤14 means that the shell 110 is stretched 4-14 times, such as 4 times, 5 times, 7 times, 8 times, 10 times, 12 times, or 14 times, etc. Considering that too much material is discharged at one time, the shell 110 is easily torn, and the dimensional stability and precision are poor, the limitation of N≥4 can make the amount of material discharged at one time not too high, thereby reducing the risk of the shell 110 being torn. Since the side wall 112 is stretched each time, the breaking elongation decreases, the structural strength decreases, and other problems occur. Therefore, the limitation of N≤14 can make the number of stretches of the shell 110 not too high, prevent the side wall 112 from being torn due to the decrease in breaking elongation, and also achieve the beneficial effects of reducing the number of steps, reducing costs, and improving the appearance of the outer surface.

[0057] Referring to Figure 4In the secondary battery 100 example, the thickness of the side wall 112 is H, the circumference of the side wall 112 is L (not shown in the figure), and LxHxSN≤2000mm 3 LxHxSN is the volume of the single discharge amount at the Nth stretching (N is any natural number greater than 2), and LxHxSN≤2000mm 3 That is, the volume of the part between each adjacent stretching line 115 is limited to be less than or equal to 2000mm 3 To limit the single discharge amount to be less than or equal to 2000mm 3 The problem of wrinkles or cracks in the side wall 112 caused by excessive single discharge amount can be improved.

[0058] Considering that the end wall 111 and the side wall 112 have a thickness difference, if the size of the connection between the end wall 111 and the side wall 112 changes suddenly, stress concentration is easy to occur at the connection between the end wall 111 and the side wall 112, and cracking occurs, in the secondary battery 100 example, please refer to Figure 3 The side wall 112 includes a variable thickness area 1121 and a uniform thickness area 1122, the variable thickness area 1121 is located between the first stretching line 115 and the end wall 111, the variable thickness area 1121 connects the end wall 111 and the uniform thickness area 1122, the variable thickness area 1121 includes a thick wall end 11211 connected to the end wall 111 and a thin wall end 11212 connected to the uniform thickness area 1122, the thickness of the thin wall end 11212 is equal to the thickness of the uniform thickness area 1122. The variable thickness area 1121 is provided at the connection between the end wall 111 and the side wall 112, which can realize the smooth transition of the end wall 111 to the side wall 112, on the one hand, it can prevent stretching cracking caused by sharp transition, on the other hand, it is beneficial to the release of internal stress, and it is beneficial to improve the strength and service life of the shell 110.

[0059] Please refer to Figure 3 Preferably, the variable thickness area 1121 and the end wall 111 are connected by a transition round corner 114, the transition round corner 114 can be tangent to the variable thickness area 1121 or connected to the variable thickness area 1121, the transition round corner 114 can be tangent to the end wall 111 or connected to the end wall 111, which is not limited, the transition round corner 114 can realize the smooth transition of the end wall 111 to the variable thickness area 1121, which can reduce the risk of cracking of the shell 110 during stretching, in addition, the secondary battery 100 needs to be placed into the tooling equipment during subsequent processes, the smooth transition round corner 114 can reduce the possibility of interference between the shell 110 and the tooling equipment.

[0060] Please refer to Figure 3In the secondary battery 100 example of the utility model, along the axial direction of the electrode assembly 120, the electrode assembly 120 includes a reaction zone 127 and two non-reaction zones 128 located on both sides of the reaction zone 127 respectively, the reaction zone 127 is the part where the first coating zone 1212 and the second coating zone 1232 coincide along the radial direction of the electrode assembly 120, during the charging and discharging process of the battery, because the first coating zone 1212 and the second coating zone 1232 in the reaction zone 127 of the electrode assembly 120 coincide along the radial direction of the electrode assembly 120, the reaction zone 127 expands cumulatively in the radial direction, the expansion force is large, which can exert a large pressure on the side wall 112. The non-reaction zone 128 is the part with only the first coating zone 1212 or only the second coating zone 1232, the non-reaction zone 128 will not expand, it should be noted that when the positive electrode tab 124 is close to the end wall 111, the non-reaction zone 128 on the side close to the end wall 111 is the part with only the first coating zone 1212, when the negative electrode tab 125 is close to the end wall 111, the non-reaction zone 128 on the side close to the end wall 111 is the part with only the second coating zone 1232; in this embodiment, the positive electrode tab 124 is close to the end wall 111, and the non-reaction zone 128 on the side close to the end wall 111 has only positive active material but no negative active material, so the non-reaction zone 128 has no lithium ion movement and will not expand.

[0061] Further, please refer to Figure 3 The distance from the boundary line between the non-reaction zone 128 on the side close to the end wall 111 and the reaction zone 127 to the inside of the end wall 111 is defined as A, and the distance from the thin-walled end 11212 to the inside of the end wall 111 is B, A≥B. It can be achieved that the reaction zone 127 does not coincide with the variable wall thickness zone 1121 but coincides with the uniform wall thickness zone 1122 of the side wall 112, which can prevent the reaction zone 127 from pressing the variable wall thickness zone 1121 first during expansion, thereby causing the shell 110 to break at the variable wall thickness zone 1121, and also can achieve that the pressure acting on the side wall 112 during the expansion of the electrode assembly 120 is uniform, thereby improving the safety performance of the battery.

[0062] The S1 distance section between the first stretching line 115 and the end wall 111 is the last time of stretching forming and is one-time stretching forming, so the stretching ratio of the S1 distance section is the highest during the last time of stretching, in the secondary battery 100 example of the utility model, please refer to Figure 3 and Figure 6 The thickness of the uniform wall thickness zone 1122 is T1, and the thickness of the end wall 111 is T2, that is, the S1 distance section reaches the thickness T1 of the uniform wall thickness zone 1122 from the thickness T2 of the end wall 111 by one-time stretching, preferably, T2 / T1≤3. For example, it can be 1, 1.5, 2, 2.5 or 3, etc., which can control the stretching ratio of the S1 distance section not to be too large, so as to reduce the probability of breaking at the S1 distance section during the last time of stretching.

[0063] Referring to Figure 1 In an example of the secondary battery 100 of the utility model, the secondary battery 100 is a cylindrical battery, the inner diameter of the shell 110 is D1, the electrode assembly 120 comprises a center hole, the diameter of the center hole is D2, when D2 / D1≤0.18, for example, it can be 0.05, 0.1, 0.12, 0.15, 0.16 or 0.18 etc., the limitation makes the battery have larger battery capacity, but the smaller the diameter D2 of the center hole is, the greater the pressure of the electrode assembly 120 on the shell 110 when swelling occurs, in the embodiment, further limit T2 / T1≥2, which means that the shell 110 needs to be stretched for many times, since there is work hardening effect in the stretching process, each stretching is beneficial to improve the hardness of the side wall 112, so that the side wall 112 can withstand greater pressure without easy breaking, thereby improving the comprehensive performance of the battery.

[0064] In an example of the secondary battery 100 of the utility model, further limit the circumferential fracture elongation rate of the side wall 112 is less than or equal to 5%, which can realize the effect that the side wall 112 is not easy to deform when the internal pressure increases, so that the battery maintains stable external dimensions, facilitating the assembly of the battery in the battery module. It should be noted that the measurement method of the circumferential fracture elongation rate is to cut the sample to be measured on the shell 110 and detect along the circumference of the shell 110 to obtain.

[0065] In an example of the secondary battery 100 of the utility model, the material of the shell 110 is steel. The steel shell has excellent properties of wear resistance, corrosion resistance, dustproof and waterproof, and can provide better protection. Referring to Figure 8 The utility model also provides an electronic device 1, electronic device 1 includes battery pack 10. The battery pack 10 includes the secondary battery 100 of any one of the above, in an embodiment of the utility model battery pack 10, referring to Figure 7 The battery pack 10 comprises a box body 101, a box cover 102 and a plurality of secondary batteries 100, the plurality of secondary batteries 100 are placed in the box body 101 and are connected in series or parallel with each other, or a mixture of series connection and parallel connection, and the box cover 102 is covered on the box body 101 to protect the plurality of secondary batteries 100. It should be noted that the battery pack 10 can also include a battery pack 10 thermal management system, a circuit board and other parts in addition to the secondary battery 100 of the utility model, the battery pack 10 can be a battery module or a battery pack, an energy storage cabinet, etc. ; Here will not be expanded one by one.

[0066] Further, the electronic device 1 further comprises a working part 11, and the working part 11 is electrically connected with the battery pack 10 to obtain power support. As an example, referring to Figure 8The electronic device 1 is a vehicle, which can be a fuel automobile, a gas automobile or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid automobile or a range extended automobile, but is not limited thereto. The working part 11 is a vehicle body, and the battery pack 10 is arranged at the bottom of the vehicle body and provides power support for driving of the vehicle or operation of electrical elements in the vehicle. However, in some other embodiments, the electronic device 1 can also be a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy and an electric tool, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The working part 11 can be a unit component capable of obtaining power of the battery pack 10 and making corresponding work, such as a fan blade rotating unit of a fan, a dust suction working unit of a dust collector, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator and an electric planer, etc. The embodiments of the present application do not specially limit the above-mentioned electronic device 1.

[0067] The secondary battery is provided with a first stretch line, a second stretch line, and an Nth stretch line, and the distance between the first stretch line and the end wall is S1, the distance between the second stretch line and the first stretch line is S2, and the distance between the Nth stretch line and the (N-1)th stretch line is SN. The S1 section, the S2 section, and the SN section of the side wall are all arranged to have a corresponding discharge amount, and the side wall has an equal wall thickness except the S1 section. Therefore, S1 is less than S2, S2 is less than SN, and the discharge amount of each time is less than that of the previous time, that is, the single discharge amount gradually decreases during the entire stretching process of the shell. This arrangement can reduce the risk of cracking of the steel shell, improve the appearance and size fluctuation of the side wall, improve the size accuracy and structural strength of the side wall, and improve the yield of the shell. Therefore, the present application effectively overcomes some practical problems in the prior art and has high utilization value and use significance. The above embodiments only exemplarily illustrate the principle and effect of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept of the present application should be covered by the claims of the present application.

Claims

1. A secondary battery characterized by comprising: The shell comprises an end wall and a side wall surrounding the end wall, the side wall and the end wall are integrally stretch formed, the side wall is formed with an opening at one end away from the end wall, and N stretch lines are arranged on the side wall along the height direction of the side wall, N being a natural number greater than 2. Wherein, along the direction from the end wall to the opening, the distance from the first stretch line to the outer surface of the end wall is S1, the distance from the second stretch line to the first stretch line is S2, and so on, the distance from the Nth stretch line to the (N-1)th stretch line is SN, S1<S2<…<SN. The side wall comprises a variable wall thickness area and a uniform wall thickness area, the variable wall thickness area is located between the first stretch line and the end wall, the variable wall thickness area connects the end wall and the uniform wall thickness area, the variable wall thickness area comprises a thick wall end connected to the end wall and a thin wall end connected to the uniform wall thickness area, and the wall thickness of the thin wall end is equal to the thickness of the uniform wall thickness area.

2. The secondary battery according to claim 1, characterized by 4≤N≤14。 3. The secondary battery according to claim 1, characterized by The thickness of the side wall is H, and the circumference of the side wall is L, wherein LxHxSN≤2000㎜ 3 .

4. The secondary battery according to claim 1, characterized by The secondary battery further comprises an electrode assembly accommodated in the shell, the electrode assembly comprises a positive electrode tab, a negative electrode tab, and a separator laminated and wound to form a wound body, the positive electrode tab comprises a first coated area coated with a positive electrode active material and a first uncoated area without the positive electrode active material, the negative electrode tab comprises a second coated area coated with a negative electrode active material and a second uncoated area without the negative electrode active material, along the axial direction of the electrode assembly, the electrode assembly comprises a reaction area and two non-reaction areas located on both sides of the reaction area, the reaction area is the part where the first coated area and the second coated area coincide in the radial direction of the electrode assembly, and the non-reaction area is the part with only the first coated area or only the second coated area, the distance from the boundary line between the non-reaction area close to the end wall side and the reaction area to the inner side of the end wall is A, and the distance from the thin wall end to the inner side of the end wall is B, wherein A≥B.

5. The secondary battery according to claim 4, characterized by The thickness of the uniform wall thickness area is T1, and the thickness of the end wall is T2, wherein T2 / T1≤3.

6. The secondary battery according to claim 4, characterized by The secondary battery is a cylindrical battery, the cylindrical battery further comprises an electrode assembly accommodated in the shell, the inner diameter of the shell is D1, the electrode assembly comprises a center hole, and the diameter of the center hole is D2, wherein when D2 / D1≤0.18, 7. The secondary battery according to claim 6, characterized by T2 / T1≥2. The circumferential breaking elongation of the side wall is less than or equal to 5%.

8. The secondary battery according to claim 7, characterized by The shell material is steel.

9. The secondary battery according to claim 8, characterized by The battery pack comprises the secondary battery of any one of claims 1 to 9.

10. An electronic device, comprising: The battery pack comprises the secondary battery of any one of claims 1 to 9.

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