Cylindrical lithium battery

Abstract

A cylindrical lithium battery. In the cylindrical lithium battery, the sum of the areas of all of second holes in a positive electrode current collector disc is 0.9-1.5 times the area of a first hole, a tail body part of the positive electrode current collector disc is provided with a fuse recess, and the minimum cross-sectional area S2 of the tail body part at the position of the fuse recess is 45%-65% of the overall cross-sectional area S1 of the tail body part. In the cylindrical lithium battery, a negative electrode current collector disc is provided with a raised platform having a flat surface, the diameter D8 of the raised platform is 28%-38% of the diameter D7 of the negative electrode current collector disc, and the height difference H4 between the surface of the raised platform and the surface of a first side is 18%-30% of the thickness T4 of the negative electrode current collector disc. By reasonably designing a narrowed neck part, the positive electrode current collector disc, and the negative electrode current collector disc, a balance is made for the cylindrical lithium battery in various aspects such as electrolyte injection performance, safety, and weldability, and battery performance can be improved.

Description

Cylindrical lithium battery Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and in particular to a cylindrical lithium battery.

[0002] Background of the Invention

[0003] Cylindrical lithium batteries are typically packaged in a cylindrical steel casing. The bare cell is manufactured using a winding process to form a cylindrical core. The cap is located at the top of the battery and is connected to the positive electrode in the core through a positive current collector. The steel casing is connected to the negative electrode in the core through a negative current collector. The positive and negative current collectors allow electrons to be transferred longitudinally from the current collector to the current collector. By increasing the current conduction area and shortening the current conduction distance, the charge and discharge performance of cylindrical lithium batteries can be effectively improved.

[0004] As mentioned earlier, in cylindrical lithium batteries, the positive current collector and negative current collector are important electrical connectors. When designing the positive current collector, many factors need to be considered, such as its electrical transmission performance, electrolyte injection, safety protection when the battery overheats, and welding processability. Therefore, how to reasonably design the positive and negative current collectors to achieve a balance in the above-mentioned aspects is an urgent problem to be solved. Summary of the Invention

[0005] This disclosure provides a cylindrical lithium battery to at least solve the technical problem of imbalance in electrolyte injection, solderability, and safety caused by unreasonable design of the positive and negative current collectors in cylindrical lithium batteries.

[0006] The first aspect of this disclosure provides a cylindrical lithium battery, including a casing, a cap, a positive current collector, a core, and a negative current collector. The positive terminal of the core is connected to the cap through the positive current collector, and the negative terminal of the core is connected to the casing through the negative current collector.

[0007] The positive current collector includes a disk body and a tail body connected to each other. The disk body is connected to the positive terminal, and the tail body is connected to the cap. The center of the disk body has a circular first hole, and at least one circular second hole is provided around the first hole. The sum of the areas of all the second holes is 0.9-1.5 times the area of ​​the first hole. At least one fuse groove is provided on the tail body. The tail body has an overall cross-sectional area S1 at the position other than the fuse groove. The tail body has a minimum cross-sectional area S2 at the position of the fuse groove. The minimum cross-sectional area S2 is 45%-65% of the overall cross-sectional area S1.

[0008] The negative current collector has a first side and a second side. The first side is connected to the negative terminal. The center of the second side has a circular and flat raised platform. The raised platform is connected to the outer shell. The diameter of the raised platform, D8, is 28%-38% of the diameter D7 of the negative current collector. The height difference H4 between the surface of the raised platform and the surface of the first side is 18%-30% of the thickness T4 of the negative current collector.

[0009] The cylindrical lithium battery according to the embodiments of this disclosure has at least the following beneficial effects:

[0010] Firstly, by rationally designing the dimensions of the first and second holes on the positive electrode current collector through which the electrolyte permeates, a balance can be achieved between electrolyte injection efficiency and weldable area, while ensuring welding safety. Furthermore, the rationally designed dimensions of the fuse groove in the tail section ensure current cutoff in the event of battery thermal runaway, thus achieving a balance between battery safety and low internal resistance in the tail section.

[0011] Secondly, by setting a flat raised platform on the side where the negative current collector connects to the inner surface of the casing, the small area of ​​the raised platform ensures good surface flatness. The surface of the raised platform can fit well with the inner surface of the casing, effectively avoiding welding quality problems such as incomplete welding. By reasonably designing the height of the raised platform, the manufacturability and usage requirements of the negative current collector are met, while the negative current collector does not occupy too much longitudinal space inside the casing, thereby improving the space utilization of the casing and further improving the performance of the battery.

[0012] In summary, by rationally designing the negative current collector of the positive current collector, the cylindrical lithium battery of this disclosure achieves a balance in multiple aspects such as safety, liquid injection performance, and weldability, and can improve battery performance.

[0013] In one possible implementation, the core has a through core hole, the diameter of the first hole D3 is 1.4-1.8 times the diameter of the core hole D6, and the diameter of the second hole D4 is 50%-70% of the diameter of the first hole D3; the flatness of the raised platform surface is 0.01-0.05mm.

[0014] By rationally designing the diameter range of the first hole, a balance can be achieved between injection efficiency and weldable area, while ensuring welding safety. Simultaneously, by rationally designing the flatness of the raised platform, its surface can fit well with the inner surface of the shell bottom, effectively preventing welding quality problems such as incomplete welds.

[0015] In one possible implementation, both the positive and negative terminals are formed by flattening the full electrode tabs, and the side of the disk body facing the positive terminal abuts against the positive terminal formed by flattening the full electrode tabs; the first side of the negative current collector abuts against the negative terminal formed by flattening.

[0016] By setting the positive and negative terminals of the core to be formed by flattening all tabs, the positive terminals are densely stacked and have a flat cross-section, avoiding wasted space in the longitudinal direction and maximizing the utilization of the internal space of the casing, which can further improve the energy density of the battery. At the same time, the positive terminal has a good fit with the positive current collector and the negative current collector, which is conducive to laser welding and can effectively reduce process defects such as incomplete welding.

[0017] In one possible implementation, the diameter D2 of the disk body is 80%-95% of the core diameter D5; the diameter D7 of the negative electrode current collector is 90%-98% of the core diameter D5.

[0018] By rationally designing the size of the positive and negative current collectors, the welding area between the two and the core can be effectively increased, thereby improving the welding effect and facilitating the design of welding tools.

[0019] In one possible implementation, the disk body is a closed axisymmetric shape consisting of a first side, an arc, a second side, and a third side connected end to end. The tail body is a closed axisymmetric shape consisting of a third side, a fifth side extending along the length of the tail body, a fourth side away from the disk body, and a sixth side extending along the length of the tail body, connected end to end. The two ends of the fifth side are connected to the fourth side and the first side, respectively, and the two ends of the sixth side are connected to the fourth side and the second side, respectively. The raised platform is integrally formed by stamping the negative electrode current collector. A recess is formed on the first side at a position corresponding to the raised platform. A welding area is formed on the first side around the recess. The surface of the welding area abuts against the negative electrode formed by flattening.

[0020] By rationally designing the shapes of the disk body and tail section, the manufacturing and assembly of the positive current collector are facilitated. Meanwhile, the negative current collector and the raised platform are formed through appropriate stamping, resulting in high dimensional accuracy and good surface quality, which facilitates welding with the core and outer shell.

[0021] In one possible implementation, the positive current collector is made of aluminum, the negative current collector is made of copper, and the surface of the negative current collector is plated with a nickel layer.

[0022] The positive current collector made of aluminum and the negative current collector made of copper have the characteristics of low internal resistance and good conductivity. In the event of thermal runaway, the positive current collector is easy to melt and cut off the current, while the nickel plating layer on the surface of the negative current collector can effectively improve the corrosion resistance of the negative current collector.

[0023] In one possible implementation, the thickness of the nickel layer is 0.08-1.5 μm.

[0024] By properly designing the thickness of the nickel layer, the corrosion resistance of the negative electrode current collector can be effectively improved.

[0025] In one possible implementation, the first width of the tail body is W1 = D2*sin(∠B / 2), and 20°≤∠B≤40°, where ∠B has its vertex at the center of the circle corresponding to the arc, and its two sides pass through the intersection points of the fifth and sixth sides with the entire circle containing the arc.

[0026] By rationally designing the width of the tail section, it is possible to retain the largest weldable area while ensuring that the tail section has sufficient mechanical strength to prevent breakage during production. In addition, it is also conducive to the rapid passage of electrons and reduces the internal resistance of the battery.

[0027] In one possible implementation, the second width W2 of the tail portion at the fuse groove is 3 / 8 to 3 / 4 of the first width W1.

[0028] When the second width W2 is too small, the tail section is not strong enough at the fuse groove and is easily broken when bent; conversely, when the second width W2 is too large, the tail section cannot fuse quickly, which poses a safety hazard. By reasonably designing the width of the tail section at the fuse groove, the mechanical performance of the tail section and the safety performance of the battery can be balanced.

[0029] In one possible implementation, the disk body has a central angle A, and 40°≤∠A≤60°; wherein, the central angle A has the center of the circle corresponding to the arc as its vertex, and the two sides pass through the endpoints of the first side away from the arc and the second side away from the arc, respectively.

[0030] By designing a reasonable center angle A, it can be ensured that the disk body still has a large solderable area after the hole is opened.

[0031] In one possible implementation, the angle θ1 between the fifth side and the first side is 45-90°, and the angle θ2 between the sixth side and the second side is 45-90°.

[0032] By rationally designing the angle θ1 between the fifth side and the first side, and the angle θ2 between the sixth side and the second side, the mechanical performance of the positive current collector and the size of the weldable area of ​​the plate body can be balanced.

[0033] In one possible implementation, the length L3 of the tail portion is 85%-95% of the diameter D2 of the disc portion.

[0034] By rationally designing the length of the tail section, a balance is achieved between welding processability and battery safety.

[0035] In one possible implementation, the outer shell includes a bottom and a sidewall. The top of the sidewall has an opening, and the sidewall is circumferentially concave near the opening to form a neck. The neck includes a first wall portion and a second wall portion extending toward the center of the outer shell. The neck also includes a connecting portion for connecting the first wall portion and the second wall portion. The outer surfaces of the first wall portion, the second wall portion, and the connecting portion together define a necking groove, and both the first wall portion and the second wall portion are inclined at a certain angle to the bottom of the shell.

[0036] In one possible implementation, the raised platform is connected to the inner surface of the shell bottom.

[0037] By setting the first and second wall portions constituting the neck to be inclined toward the bottom of the shell, the neck has a certain amount of slump allowance. Therefore, it is convenient to design the grooving in the preceding grooving process, and to form the required neck structure in the sealing process.

[0038] In one possible implementation, the larger of the angle between the first wall and the bottom of the shell and the angle between the second wall and the bottom of the shell is α, satisfying that α < 10°.

[0039] By rationally designing the included angle α, the design difficulty of the groove is reduced, while the impact of the necking on the lower cavity space is minimized and the sealing effect on the cap is ensured.

[0040] In one possible implementation, the included angle α satisfies: 1° < α < 5°.

[0041] By rationally designing the included angle α, the design difficulty of the groove is reduced, while the impact of the necking on the lower cavity space is minimized and the sealing effect on the cap is ensured.

[0042] In one possible implementation, the dimension L5 of the fuse groove along the length of the tail section is 0 < L5 ≤ W1, where W1 is the first width of the tail section; the depth H3 of the necking groove in the radial direction is 5%-10% of the outer diameter D1 of the outer shell.

[0043] If L5 is too large, the location of the fuse at the tail section becomes difficult to determine, increasing the battery's safety risk. Conversely, if L5 is too small, the fuse sensitivity at the tail section increases, potentially causing the fuse to blow even at a safe current. Properly designing the size of the fuse groove helps improve battery safety. Simultaneously, by appropriately designing the depth of the necking groove on the casing, the internal space utilization of the casing can be effectively improved to increase the battery's energy density. Furthermore, it can also improve the structural strength of the necking groove and the sealing process.

[0044] In one possible implementation, the dimension L5 of the fuse groove along the length of the tail portion is 1 / 4 to 3 / 4 of the first width W1 of the tail portion; the minimum wall thickness T2 of the neck is 0.1-0.2 mm, and the minimum wall thickness T2 of the neck is more than 80% of the wall thickness T1 of the side wall.

[0045] By properly designing the dimensions of the fuse groove, battery safety can be improved. At the same time, by properly designing the wall thickness at the thinnest point of the neck, the pressure resistance of the casing can be ensured to meet requirements.

[0046] In one possible implementation, the distance L1 from the lowest point of the neck to the upper surface of the shell bottom is 90%-98% of the height H1 of the shell, and the height H2 of the neck groove is 0.1%-1% of the height H1 of the shell.

[0047] By rationally designing the depth of the necking groove on the casing, the utilization rate of the internal space of the casing can be effectively improved, thereby increasing the energy density of the battery.

[0048] In one possible implementation, the distance L4 between the center of the fuse groove and the end of the tail portion away from the disc portion is 68%-78% of the length L3 of the tail portion.

[0049] Brief description of the attached figures

[0050] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments of this disclosure will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 is an exploded view of a cylindrical lithium battery according to an embodiment of the present disclosure;

[0052] Figure 2 is a cross-sectional schematic diagram of the connection between the outer casing and the cap in a cylindrical lithium battery according to an embodiment of the present disclosure;

[0053] Figure 3 is a partial schematic diagram of point A in Figure 2;

[0054] Figure 4 is a cross-sectional schematic diagram of the cap in a cylindrical lithium battery according to an embodiment of the present disclosure;

[0055] Figure 5 is a top view of the positive electrode current collector in a cylindrical lithium battery according to an embodiment of the present disclosure, wherein the tail portion is in an unfolded state.

[0056] Figure 6 is a schematic diagram of the connection between the positive current collector and the winding core in Figure 5;

[0057] Figure 7 is a schematic diagram of the tail section of the positive current collector in Figure 5;

[0058] Figure 8 is a schematic diagram of the cross section along direction AA in Figure 7;

[0059] Figure 9 is a schematic diagram of the tail section of the positive current collector in Figure 5;

[0060] Figure 10 is a schematic diagram of the structure in which the negative electrode current collector is connected to the core and the bottom of the casing in a cylindrical lithium battery according to an embodiment of the present disclosure.

[0061] Figure 11 is a cross-sectional schematic diagram of the negative current collector in Figure 10;

[0062] Figure 12 is a partial schematic diagram of point B in Figure 11.

[0063] Reference numerals: 110-outer shell, 111-shell bottom, 112-side wall, 1121-neck, 1121a-first wall portion, 1121b-second wall portion, 1121c-connecting portion, 1122-rolled edge, 1123-necked groove, 113-inner cavity, 1131-upper cavity, 1132-lower cavity, 114-opening; 120-cap, 121-top cover, 122-explosion-proof valve plate, 123-insulating plate, 124-terminal plate, 125-insulating ring; 130-Positive current collector, 131-Disc body, 1311-First side, 1312-Arc, 1313-Second side, 1314-Third side, 1315-First hole, 1316-Second hole, 132-Tail body, 1321-Fuse groove, 1322-Fifth side, 1323-Sixth side, 1324-Fourth side; 140-Core, 141-Positive end, 142-Negative end, 143-Core hole; 150-Negative current collector, 151-First side, 1511-Recessed part, 1512-Welding area, 152-Second side, 1521-Elevated platform.

[0064] Methods of implementing the present invention

[0065] The embodiments of this implementation are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this implementation, and should not be construed as limiting this implementation.

[0066] In the description of this embodiment, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this embodiment and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this embodiment.

[0067] In the description of this embodiment, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0068] In the description of this embodiment, unless otherwise explicitly limited, terms such as setting, installing, and connecting should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this embodiment in conjunction with the specific content of the technical solution.

[0069] The cylindrical lithium battery provided in this disclosure includes various size series, such as the 21 series (cylindrical lithium battery with an outer diameter of 21 mm) and the 46 series (cylindrical lithium battery with an outer diameter of 46 mm), and is not limited herein. Specifically, as shown in FIG1, the cylindrical lithium battery includes a casing 110, a cap 120, a positive current collector 130, a core 140, and a negative current collector 150. The positive terminal 141 of the core 140 is connected to the cap 120 through the positive current collector 130, and the negative terminal 142 of the core 140 is connected to the casing 110 through the negative current collector 150, so that the cap 120 serves as the positive electrode of the cylindrical lithium battery, and the casing 110 serves as the negative electrode of the cylindrical lithium battery for electrical connection with external electrical equipment.

[0070] The following is a detailed description of the casing 110.

[0071] As shown in Figures 1 and 2, the outer shell 110 is cylindrical in shape and is closed on the negative electrode side (lower part in Figure 1) and open on the positive electrode side (upper part in Figure 1). Specifically, the outer shell 110 includes a bottom 111 and a sidewall 112. The bottom 111 is circular, and the sidewall 112 extends upward along the edge of the bottom 111. The bottom 111 and the sidewall 112 together define an inner cavity 113. The top of the sidewall 112 has an opening 114 that communicates with the inner cavity 113.

[0072] The inner cavity 113, defined by the bottom 111 and the sidewall 112, is also cylindrical and is used to accommodate the cap 120 (whose top is exposed), the positive current collector 130, the core 140, and the negative current collector 150, which will be described below. Furthermore, by setting the outer casing 110 to be open at the top, i.e., by providing an opening 114 at the top of the outer casing 110, it is also convenient for the aforementioned components to enter the outer casing 110 through the opening 114.

[0073] The bottom of the shell 111 is in the shape of a thin circular plate. The bottom surface of the negative electrode current collector 150 is in contact with the inner surface of the bottom of the shell 111, thereby forming a conductive connection between the two, thus connecting the outer shell 110 and the negative electrode of the core 140.

[0074] The outer casing 110 can be made of nickel-plated steel, which has advantages such as high pressure resistance. Of course, it is not limited to this; for example, it can also be made of aluminum. The following explanation uses the case of nickel-plated steel casing 110 as an example. It can be stamped from steel strip, which is simple to process and manufacture, easy to mass-produce, and can effectively reduce costs.

[0075] As shown in Figures 2 and 3, the sidewall 112 is concave inward along the circumference near the opening 114 to form a constricted neck 1121 for sealing the cap 120. The constricted neck 1121 divides the inner cavity 113 into two parts: an upper cavity 1131 and a lower cavity 1132. It can be formed by grooving and sealing processes. In the sealing process, in addition to the concave neck 1121, the sidewall 112 also forms a rolled edge 1122 at the top. The rolled edge 1122, together with the constricted neck 1121 and the sidewall 112, achieves a sealing connection for the cap 120. Specifically, the top surface of the constricted neck 1121, located on one side of the upper cavity 1131, is used to receive the cap 120 and is in contact with the bottom of the cap 120. The inner wall surface of the portion of the side wall 112 located between the constricted neck 1121 and the rolled edge 1122 is in contact with the outer peripheral surface of the cap 120, while the inner wall surface of the rolled edge 1122 is in contact with the top surface of the cap 120. Thus, the cap 120 completely closes the opening 114, sealing the negative electrode current collector 150, the rolled core 140, and the positive electrode current collector 130 in the lower cavity 1132, thereby forming a closed electrochemical system within the outer casing 110.

[0076] Specifically, the neck 1121 includes a first wall portion 1121a and a second wall portion 1121b, which are flat and parallel to each other and extend toward the center of the inner cavity 113, and a connecting portion 1121c for connecting the first wall portion 1121a and the second wall portion 1121b. In the direction shown in FIG2, the first wall portion 1121a is located above the second wall portion 1121b, and the ends of the first wall portion 1121a and the second wall portion 1121b near the center of the inner cavity 113 are connected by the connecting portion 1121c. The outer surfaces of the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c together define a necking groove 1123. The inner surface (i.e., the top surface) of the first wall portion 1121a is used to receive the cap 120 and is in contact with the bottom of the cap 120.

[0077] Although the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c are described above as being interconnected, these three portions are themselves part of the side wall 112. During the sealing process, the side wall 112 undergoes inward plastic deformation at the position corresponding to the neck 1121, thereby forming the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c; that is, the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c are integral. Of course, in a preceding process before sealing, a groove can be cut at this position, for example, through the feed motion of a cutting roller and the rotational motion of the outer casing 110, so that during sealing, the groove undergoes plastic deformation to form the required neck 1121.

[0078] In this embodiment, both the first wall portion 1121a and the second wall portion 1121b are flat, and they are inclined towards the bottom of the shell 111 along their concave direction. Specifically, when the first wall portion 1121a and the second wall portion 1121b are parallel to each other, the angle between the first wall portion 1121a or the second wall portion 1121b and the bottom of the shell 111 is α, satisfying α < 10°. In this case, since the first wall portion 1121a and the second wall portion 1121b are both flat and parallel to each other, that is, the central plane of the necking groove 1123 defined by the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c is inclined to the surface of the bottom of the shell 111, and the inclination angle is not greater than 10°.

[0079] When the first wall portion 1121a and the second wall portion 1121b are not completely parallel, the larger of the angles between the first wall portion 1121a or the second wall portion 1121b and the shell bottom 111 is α, satisfying α < 10°. In this case, since the first wall portion 1121a and the second wall portion 1121b are not completely parallel, the angles α between the first wall portion 1121a and the shell bottom 111, and between the second wall portion 1121b and the shell bottom 111, are both less than 10°.

[0080] Therefore, firstly, by setting the first wall portion 1121a and the second wall portion 1121b constituting the neck 1121 to be inclined towards the bottom of the shell 111, the neck 1121 has a certain amount of sag allowance. Therefore, it is convenient to design the grooving in the preceding grooving process, and it is convenient to form the required neck structure in the sealing process. Secondly, the inclination angle of the first wall portion 1121a and the second wall portion 1121b does not exceed 10°, and the height of the neck 1121 entering the lower cavity 1132 is small, which ensures the effective space of the lower cavity 1132 and also avoids damage to the core electrode assembly. Furthermore, since the tilt angle of the first wall portion 1121a and the second wall portion 1121b does not exceed 10°, the top surface of the constricted neck 1121 in the inner cavity 113 (that is, the top surface of the first wall portion 1121a) is basically horizontal, and its contact area with the bottom surface of the cap 120 is large. There is sufficient compression between the two, resulting in a good sealing effect and improving the safety of the lithium battery.

[0081] Furthermore, in some embodiments, the included angle α satisfies: 1° < α < 5°. The included angle α affects the design difficulty of the groove, the utilization rate of the internal space of the outer shell 110, and the sealing effect of the cap 120. If α is too large, although the design difficulty of the groove is small, the utilization rate of the internal space of the outer shell 110 will be reduced, and the sealing effect of the cap 120 will be worse. Conversely, if α is too small, the groove is difficult to design, and the necking 1121 is difficult to form. By reasonably designing the size of the included angle α, the design difficulty of the groove is reduced, while the impact of the necking 1121 on the space of the lower cavity 1132 can be reduced and the sealing effect of the cap 120 can be ensured.

[0082] In some embodiments, the distance L1 from the lowest point of the neck 1121 in the inner cavity 113 to the upper surface of the bottom shell 111 is defined as L1, and the height of the outer shell 110 is defined as H1, satisfying the condition: 90% ≤ L1 / H1 ≤ 98%. If the distance L1 from the lowest point of the neck 1121 to the upper surface of the bottom shell 111 is too large, i.e., L1 / H1 is too large, it will affect the height of the upper cavity 1131, resulting in a poorer sealing effect. Conversely, if the distance L1 from the lowest point of the neck 1121 to the upper surface of the bottom shell 111 is too small, i.e., L1 / H1 is too small, it will affect the height of the lower cavity 1132, thus wasting the height of the outer shell 110 and reducing the energy density of the battery. By rationally designing the distance L1 from the lowest point of the neck 1121 in the inner cavity 113 to the upper surface of the bottom shell 111, the sealing effect at the seal can be ensured while also improving the utilization rate of the internal space of the outer shell 110 and increasing the energy density of the battery.

[0083] Furthermore, in some embodiments, the height of the necking groove 1123 is defined as H2, and the height of the outer casing 110 is defined as H1, wherein 0.1% ≤ H2 / H1 ≤ 1%. If the height H2 of the necking groove 1123 is too large, the height of the outer casing 110 will be wasted, resulting in a decrease in the energy density of the lithium battery; conversely, if the height H2 of the necking groove 1123 is too small, the stress at the connection 1121c is prone to concentration, the necking 1121 may break at this location, and the sealing process will be more difficult, leading to a decrease in yield. By reasonably designing the height H2 of the necking groove 1123, while ensuring that the structural strength of the necking 1121 meets the requirements, the utilization rate of the internal space of the outer casing 110 and the manufacturability of the sealing process can also be effectively improved. As shown in Figure 3, the height H2 described here refers to the height of the opening of the necking groove 1123. Of course, if the first wall portion 1121a and the second wall portion 1121b are set to be parallel, then the height inside the necking groove 1123 will be consistent with this height H2. More preferably, 0.2% ≤ H2 / H1 ≤ 0.5%.

[0084] In some embodiments, the depth of the constriction groove 1123 in the radial direction is H3, and the outer diameter of the outer shell 110 is D1, wherein 5% ≤ H3 / D1 ≤ 10%. If the depth H3 of the constriction groove 1123 is too large, i.e., H3 / D1 is too large, the constriction neck 1121 will excessively intrude into the inner cavity 113 in the radial direction, resulting in a smaller inner diameter of the inner cavity 113 at the constriction neck 1121, causing wasted space, and also weakening the structural rigidity of the constriction neck 1121 itself, increasing stress, and posing a risk of cracking, thereby failing to guarantee the sealing performance; conversely, if the depth H3 of the constriction groove 1123 is too small, i.e., H3 / D1 is too small, the cap 120 cannot be stably supported by the first wall portion 1121a, and the dimensional chain matching between the two is poor. When sealing, the cap 120 may directly pass through the groove defined by the constriction neck 1121 and enter the lower cavity 1132. By rationally designing the depth H3 of the necking groove 1123, while ensuring that the cap 120 can be stably supported by the first wall portion 1121a to facilitate smooth sealing, the utilization rate of the internal space of the outer casing 110 can also be improved, further increasing the energy density of the lithium battery.

[0085] During the sealing process, the wall thicknesses of the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c change due to plastic deformation of the material. To ensure the pressure resistance of the outer shell 110, in some embodiments, the minimum wall thickness of the neck 1121 is defined as T2, and the wall thickness of the outer shell 110 is defined as T1, wherein T2 / T1 ≥ 80%, more preferably, T2 / T1 ≥ 85%. This minimum wall thickness T2 may occur at any one of the first wall portion 1121a, the second wall portion 1121b, and the connecting portion 1121c. If T2 / T1 is less than 80%, the safety margin for the mechanical strength of the outer shell 110 is insufficient. For example, when the internal air pressure of the outer shell 110 increases, it may cause the outer shell 110 to tear at that point. By rationally designing the wall thickness T2 at the thinnest point of the neck 1121, the pressure resistance of the outer shell 110 can be ensured to meet the requirements.

[0086] In some embodiments, to ensure the pressure resistance of the housing 110, the minimum wall thickness of the neck 1121 is set as T2, where 0.1 mm ≤ T2 ≤ 0.2 mm. Setting the minimum wall thickness T2 of the neck 1121 between 0.1 and 0.2 mm allows the neck 1121 to meet the pressure resistance requirements of housings 110 with common wall thicknesses. For example, for a housing 110 with a wall thickness of 0.2 mm, the minimum wall thickness T2 of the neck 1121 can be 0.17 mm.

[0087] The following is a detailed introduction to the 120-point block.

[0088] The cap 120 and the outer casing 110 together act as a physical barrier to isolate the active material of the cylindrical lithium battery from the outside world. Furthermore, when the gas pressure inside the battery exceeds a preset value, the explosion-proof valve 122 of the cap 120 opens to release the pressure, thereby preventing the battery from deforming, bulging, or even burning or exploding.

[0089] As shown in Figure 4, the cap 120 includes a top cover 121, an explosion-proof valve plate 122, an insulating plate 123, a terminal plate 124, and an insulating ring 125 located on the outer edge. The top cover 121, the explosion-proof valve plate 122, and the terminal plate 124 are stacked sequentially from top to bottom and are electrically connected to each other. After the cap 120 is sealed to the outer casing 110, the top cover 121 protrudes outside the outer casing 110 and serves as the positive terminal for electrical connection with the positive terminal of external electrical equipment. The bottom surface of the terminal plate 124 is connected to the positive current collector 130, for example, by welding the positive current collector 130 to the terminal plate 124, thereby forming a conductive connection between the two, thus connecting the top cover 121 to the positive terminal 141 of the core 140.

[0090] The following is a detailed introduction to the positive current collector 130.

[0091] As shown in Figures 5 and 6, the positive current collector 130 includes a disc body portion 131 and a tail body portion 132 connected to each other. The disc body portion 131 is used to connect to the positive terminal 141 of the core 140, and the tail body portion 132 is used to connect to the cap 120, so that a passage is formed between the core 140 and the cap 120. In this disclosure, the connection between the disc body portion 131 and the core 140, and the connection between the tail body portion 132 and the cap 120, can adopt any connection method well known to those skilled in the art, such as welding; the connection between the tail body portion 132 and the disc body portion 131 can be any fixed connection method, but to ensure the stability of the connection and structural strength, an integral connection is preferred.

[0092] As shown in Figure 5, in order to match the circular cross-section of the core 140 and facilitate welding between the disc body 131 and the core 140, the disc body 131 is a closed axisymmetric figure composed of a first side 1311, an arc 1312, a second side 1313, and a third side 1314 connected end to end. The tail body 132 includes a fifth side 1322 and a sixth side 1323 along its length, and a fourth side 1324 away from the disc body 131. The two ends of the fifth side 1322 are connected to the fourth side 1324 and the first side 1311, respectively, and the two ends of the sixth side 1323 are connected to the fourth side 1324 and the second side 1313, respectively. Thus, as seen in Figure 5, the tail body 132 extends from one end of the disc body 131 and is also a closed axisymmetric figure. It should be noted that the third side 1314 is a virtual edge line proposed for the convenience of describing the disk portion 131. This side does not exist in the actual product, so it is marked with a dashed line in Figure 5 to distinguish it. In addition, referring to Figures 1 and 6, when the positive electrode current collector 130 is assembled into the cylindrical lithium battery, the tail portion 132 bends, and its far end will be located above the closed axisymmetric shape formed by the disk portion 131.

[0093] To improve the efficiency of electrolyte injection during battery production, the disc portion 131 typically has holes through which the electrolyte passes. To ensure that the solid area of ​​the disc portion 131 still accounts for more than 75% of its total area after drilling, facilitating welding to the core 140, the disc portion 131 has a central angle A, where 40°≤∠A≤60°, and more preferably 45°≤∠A≤55°. Specifically, the total area of ​​the disc portion 131 is the sum of its solid area and the area of ​​the holes; the central angle A has its vertex at the center of the circle corresponding to arc 1312, and its two sides pass through the endpoints of the first side 1311 and the second side 1313 that are away from arc 1312, respectively. The endpoints of the first side 1311 and the second side 1313 that are furthest from the arc 1312 are also the connection points between the first side 1311, the second side 1313 and the tail body 132.

[0094] In some embodiments, the diameter D2 of the disc portion 131 is 80%-95% of the diameter D5 of the core 140, where the diameter D2 of the disc portion 131 refers to the longest line segment between two points on the arc 1312, and the diameter D5 of the core 140 refers to the diameter of the circular cross-section of the core 140. Depending on actual needs, the diameter D2 of the disc portion 131 is, for example, 15-23 mm. Within the preferred diameter range, the disc portion 131 ensures a large contact area between itself and the core 140, increasing the weldable area and expanding the adaptability of the weld wire length and shape. When the contact area of ​​the negative electrode current collector 150 is large, within the aforementioned diameter range, the positive electrode current collector 130 will not become a bottleneck limiting the charge and discharge performance of the cylindrical lithium battery.

[0095] In some embodiments, a first hole 1315 is provided at the center of the disc portion 131 for injecting electrolyte into the battery. The center of the disc portion 131 may be the center of a circle corresponding to the arc 1312. The core 140 is manufactured by a winding process, and a circular core hole 143 is formed at the center of the core 140 after winding. To match the shape of the core hole 143, the first hole 1315 is preferably circular.

[0096] In some embodiments, the diameter D3 of the first hole 1315 is 1.4-1.8 times the diameter D6 of the core hole 143 of the core 140. Depending on actual needs, the diameter D3 of the first hole 1315 can be, for example, 4-8 mm. Within this diameter range, the first hole 1315 can achieve a balance between liquid injection efficiency and weldable area, while ensuring welding safety. If the diameter D3 of the first hole 1315 is too small, it will hinder liquid wetting, and when using resistance welding at the bottom of the battery, the electrode tip extending into the core hole 143 of the core 140 may make undesirable contact with the current collector, posing an interference risk. If the diameter D3 of the first hole 1315 is too large, the weldable area will be correspondingly reduced, limiting the welding processability between the disc body 131 and the core 140.

[0097] In some embodiments, the diameter D3 of the first hole 1315 is 25%-35% of the diameter D2 of the disc portion 131. Depending on actual needs, the diameter D3 of the first hole 1315 is, for example, 4-8 mm. Within this diameter range, the first hole 1315 achieves a balance between liquid injection efficiency and weldable area, while ensuring welding safety. If the diameter D3 of the first hole 1315 is too small, it is not conducive to liquid wetting, and when using resistance welding at the bottom of the battery, the electrode tip extending into the core hole 143 of the core 140 may make undesirable contact with the current collector, posing an interference risk. If the diameter D3 of the first hole 1315 is too large, the weldable area is correspondingly reduced, limiting the welding process between the disc portion 131 and the core 140.

[0098] In some embodiments, at least one second hole 1316 is provided around the periphery of the first hole 1315 to assist electrolyte wetting. Preferably, the second hole 1316 is a circular hole. More preferably, the area of ​​a single second hole 1316 is 0.3-0.5 times the area of ​​the first hole 1315, and the sum of the areas of all second holes 1316 is 0.9-1.5 times the area of ​​the first hole 1315. If the area of ​​the second hole 1316 is too small compared to the area of ​​the first hole 1315, the auxiliary wetting effect will be insignificant; if the area of ​​the second hole 1316 is too large, the solderable area of ​​the disc portion 131 will be significantly reduced, affecting the connection between the disc portion 131 and the core 140.

[0099] In some embodiments, the distance L2 between the center of the second hole 1316 and the center of the first hole 1315 is 25%-35% of the diameter D2 of the disk portion 131. Depending on actual needs, L2 is, for example, 4.5-7 mm. By rationally designing the distance L2 between the second hole 1316 and the first hole 1315, it is helpful to improve the wetting effect of the electrolyte while ensuring the area of ​​the solderable region. If the distance L2 between the second hole 1316 and the first hole 1315 is too small, the wetting effect of the electrolyte cannot be significantly improved; if the distance L2 between the second hole 1316 and the first hole 1315 is too large, the second hole 1316 will be too close to the edge of the disk portion 131, thereby restricting the battery encapsulation. If the encapsulation blocks the second hole 1316, the electrolyte cannot be injected through the second hole 1316.

[0100] For ease of processing and improved yield, in a preferred embodiment, the diameter D4 of the second hole 1316 is 50%-70% of the diameter D3 of the first hole 1315, and the diameter D4 of the second hole 1316 is, for example, 2-4.8 mm. If the diameter D4 of the second hole 1316 is smaller than the preferred diameter range, it is difficult to achieve the auxiliary wetting effect; if the diameter D4 of the second hole 1316 is larger than the preferred diameter range, the weldable area of ​​the disc body 131 is reduced. The number of second holes 1316 can be determined according to the actual welding process. The number of welding areas is n, and the number of second holes 1316 is n-1, where n≥2.

[0101] The disk portion 131 will be further described below with reference to embodiments and comparative examples. The embodiments and comparative examples described below are designed with reference to a common 21 series cylindrical lithium battery.

[0102] Example 1:

[0103] Example 1 provides a cylindrical lithium battery, comprising a casing 110, a cap 120, a positive current collector 130, a core 140, and a negative current collector 150. The positive current collector 130 includes an interconnected disk body portion 131 and a tail portion 132. The disk body portion 131 is connected to the positive terminal 141 of the core 140, and the tail portion 132 is connected to the cap 120. The disk body portion 131 has a circular first hole 1315 at its center, and multiple similarly circular second holes 1316 are provided around the periphery of the first hole 1315. Furthermore, the shape of the disk body portion 131 is a closed axisymmetric figure formed by sequentially connecting a first side 1311, an arc 1312, a second side 1313, and a third side 1314, with a central angle B.

[0104] Wherein, the diameter D5 of the core 140 is 20mm; the diameter D2 of the disc body 131 is 85% of the diameter D5 of the core 140; the diameter D3 of the first hole 1315 is 30% of the diameter D2 of the disc body 131; the diameter D4 of the second hole 1316 is 60% of the diameter D3 of the first hole 1315; the sum of the areas of all the second holes 1316 is 1.2 times the area of ​​the first hole 1315; the distance L2 between the center of the second hole 1316 and the center of the first hole 1315 is 30% of the diameter D2 of the disc body 131; and the included angle B of the center of the disc body 131 is 35°.

[0105] Comparative Example 1:

[0106] Comparative Example 1 provides a cylindrical lithium battery that differs from Example 1 in that the sum of the areas of all the second holes 1316 is 0.4 times the area of ​​the first hole 1315.

[0107] Comparative Example 2:

[0108] Comparative Example 2 provides a cylindrical lithium battery, which differs from Example 1 in that the diameter D3 of the first hole 1315 is 10% of the diameter D2 of the disk portion 131.

[0109] Table 1 below evaluates the electrolyte wetting effect of the sealed cylindrical lithium batteries produced in the above embodiments and comparative examples. The specific electrolyte wetting test method is as follows: Samples of the casing 110, cap 120, positive electrode current collector 130, core 140, negative electrode current collector 150, and electrolyte were taken. The positive electrode current collector 130 and negative electrode current collector 150 were welded to the core 140. After placing the assembly into the casing 100, the cap 120 was welded again, resulting in an unsealed cylindrical lithium battery. Next, the cylindrical lithium battery was placed in an electrolyte injection device for injection, with an injection volume of 6.8g. After positive and negative pressure cycling of the device, the cylindrical lithium battery was mechanically sealed. After standing for 1 hour, the cylindrical lithium battery was disassembled, the core 140 was removed and unfolded, and placed on a CCD detection device for photographing. The wetting area was depicted, and the device program was started to calculate the wetting area S0. With the total electrode area set as S, the wetting rate was S0 / S.

[0110] Table 1

[0111] As shown in Table 1, when the sum of the areas of all the second holes 1316 is 1.2 times the area of ​​the first hole 1315, and the diameter D3 of the first hole 1315 is 30% of the diameter D2 of the disc body 131, the electrolyte wetting effect of the core 140 is better. However, if the sum of the areas of all the second holes 1316 is too low or the area of ​​the first hole 1315 is too small, the electrolyte wetting effect of the core 140 will be worse.

[0112] Referring again to Figure 5, in some embodiments, at least one fuse groove 1321 is formed on the tail section 132. By designing the fuse groove, the width of the tail section 132 at the fuse groove 1321 is reduced. During battery thermal runaway, current converges at this location, heat rises and reaches the melting point, causing the tail section 132 to melt and achieve the current interruption effect. Specifically, the shape of the fuse groove 1321 can be any shape, such as trapezoidal, rectangular, U-shaped, V-shaped, or semi-circular. This disclosure does not limit the number of fuse grooves 1321; the figures exemplarily show two symmetrically arranged fuse grooves 1321. When there are multiple fuse grooves 1321, all fuse grooves 1321 can be of the same shape or different shapes. In principle, the arrangement of the fuse grooves 1321 must simultaneously ensure the melting effect and mechanical strength of the tail section 132.

[0113] In some embodiments, as shown in FIG7, the distance L4 between the center of the fuse groove 1321 and the end of the tail portion 132 away from the disc portion 131 is 68%-78% of the length L3 of the tail portion 132. Depending on actual needs, the distance between the center of the fuse groove 1321 and the end of the tail portion 132 away from the disc portion 131 is, for example, 8-18 mm. If the shape of the fuse groove 1321 is a simple graphic, the center of the fuse groove 1321 can be a location recognized by those skilled in the art. For example, for a trapezoidal or rectangular fuse groove 1321, the center can be the intersection of two diagonals; for a semi-circular fuse groove 1321, the center can be the center of the circle. If the shape of the fuse groove 1321 is more complex or irregular, the center of the fuse groove 1321 is the geometric center of its shape, that is, the average position of all points in the shape. This can be determined by any method mastered by those skilled in the art, such as integration, discrete point method, graphic segmentation method, or directly calculated using software tools. The length L3 of the tail section 132 is the distance from the connection point between the tail section 132 and the disk section 131 to the end of the tail section 132 away from the disk section 131. The fuse groove 1321 is positioned appropriately to ensure smooth welding between the tail section 132 and the cap 120, while also ensuring current cutoff in the event of battery thermal runaway. If the distance between the fuse groove 1321 and the end of the tail section 132 away from the disk section 131 is too small, the fuse groove 1321 will be too close to the welding position, and the welding between the tail section 132 and the cap 120 will be interfered with; conversely, if the distance between the fuse groove 1321 and the disk section 131 is too close, the current path at the fuse groove 1321 will be large, and if there is overcurrent, it will not be able to melt in time, increasing the safety risk of the battery.

[0114] In some embodiments, to improve battery safety, the length L3 of the tail portion 132 is 85%-95% of the diameter of the disc portion 131. Depending on actual needs, the length of the tail portion 132 is, for example, 12-20 mm. Within the preferred length range, the tail portion 132 ensures both smooth welding with the cap 120 and battery safety. If the tail portion 132 is too short, it will not extend sufficiently beyond the outer casing 110 after a single bend, making welding with the cap 120 impossible. If the tail portion 132 is too long, the end of the tail portion 132 away from the disc portion 131 will contact the outer casing 110 during a second bend of the cap 120, causing a short circuit in the battery and occupying internal battery space, affecting the installation and normal operation of other components.

[0115] For ease of bending and welding, the tail portion 132 is typically elongated. In some embodiments, the tail portion 132 has a first width W1, satisfying: W1 = D2 * sin(∠B / 2), where D2 is the diameter of the disc portion 131, which is the longest line segment between two points on the arc 1312. Depending on actual needs, the diameter of the disc portion 131 is, for example, 15-23 mm. Furthermore, the included angle B is with the center of the circle corresponding to the arc 1312 as the vertex, and the two sides pass through the intersection points of the fifth side 1322 and the sixth side 1323 of the tail portion 132 with the entire circle containing the arc 1312 (refer to Figure 5). For example, 20° ≤ ∠B ≤ 40°. The larger the first width W1 of the tail portion 132, the smaller the weldable area of ​​the disc portion 131 will be. A reasonable width design helps to retain the largest weldable area, while ensuring that the tail portion 132 has sufficient mechanical strength to prevent it from being broken during production. At the same time, it is conducive to the rapid passage of electrons and reduces the internal resistance of the battery.

[0116] In some embodiments, the tail portion 132 has a second width W2 at the fuse groove 1321, and 3W1 / 8 ≤ W2 < 3W1 / 4, that is, the second width W2 is 3 / 8 to 3 / 4 of the first width W1. In this disclosure, the second width W2 refers to the change in width of the tail portion 132 relative to the first width W1 at this location due to the design of the fuse groove 1321. Based on the definition of the second width W2 in this disclosure, the first width W1 in this disclosure refers to the width of the tail portion 132 at locations other than the fuse groove 1321. A second width W2 at the fuse groove 1321 within a reasonable range can balance the mechanical properties of the tail portion 132 and the safety performance of the battery. When the second width W2 is too small, the tail portion 132 lacks sufficient strength at the fuse groove 1321 and is easily broken when bent.

[0117] In some embodiments, the dimension L5 of the fuse groove 1321 along the length of the tail portion 132 satisfies: 0 < L5 ≤ W1, that is, the length of the fuse groove 1321 in the vertical direction does not exceed the first width W1 of the tail portion 132. Preferably, W1 / 4 < L5 ≤ 3W1 / 4, that is, the dimension L5 is 1 / 4 to 3 / 4 of the first width W1. In this disclosure, the dimension of the fuse groove 1321 along the length of the tail portion 132 refers to the length between the end of the fuse groove 1321 closest to the disc portion 131 and the end of the fuse groove 1321 farthest from the disc portion 131. A reasonable dimension of the fuse groove 1321 along the length of the tail portion 132 helps improve battery safety. If the dimension is too large, the melting position of the tail portion 132 is difficult to determine, thereby increasing the safety risk of the battery; conversely, if the dimension is too small, the melting sensitivity of the tail portion 132 increases, and there is a possibility of melting even at a safe current.

[0118] In some embodiments, as shown in FIG8, the minimum cross-sectional area S2 of the tail portion 132 at the fuse groove 1321 is 45%-65% of the overall cross-sectional area S1 of the tail portion 132. Specifically, the minimum cross-sectional area S2 of the tail portion 132 at the fuse groove 1321 is the cross-sectional area at the narrowest position of the fuse groove 1321. For example, as shown in FIG10, when the cross-section at this position is square, its cross-sectional area S2 = W2 * T3; the overall cross-sectional area S1 of the tail portion 132 is the cross-sectional area at the position of the tail portion 132 other than the fuse groove 1321, S1 = W1 * T3, where T3 is the thickness of the tail portion 132, which is usually a uniform thickness. Depending on the actual needs, T3 is, for example, 0.15-0.35 mm. Within a reasonable minimum cross-sectional area S2 range, the tail portion 132 can achieve a balance between battery safety and low internal resistance. When the minimum cross-sectional area S1 is too large, the tail portion 132 cannot quickly melt and break in the event of thermal runaway, increasing the safety risk. Conversely, when the minimum cross-sectional area S2 is too small, on the one hand, the melting sensitivity will be too high, and on the other hand, the internal resistance will increase, seriously affecting the normal use of the battery. Of course, in the above calculation of S1 and S2, the thickness of the tail portion 132 at the melting groove 1321 is the same as the thickness of the rest of the portion, that is, the tail portion 132 is of equal thickness. However, it is not limited to this, and the thicknesses of the two can also be set to be different.

[0119] As shown in Figure 9, the tail portion 132 includes a fifth side 1322 and a sixth side 1323 along its length, and a fourth side 1324 away from the disc portion 131. The two ends of the fifth side 1322 are connected to the fourth side 1324 and the first side 1311, respectively. The two ends of the sixth side 1323 are connected to the fourth side 1324 and the second side 1313, respectively. The angle θ1 between the fifth side 1322 and the first side 1311 is 45-90°, and the angle θ2 between the sixth side 1323 and the second side 1313 is 45-90°. If the angles θ1 and θ2 are too small, the bending of the tail portion 132 will cause the stress to be too concentrated at the angles θ1 and θ2, causing the disc portion 131 to deform or even crack. If the angles θ1 and θ2 are too large, it cannot be guaranteed that the disc portion 131 has sufficient weldable area. In addition, the reasonable angle design of the included angles θ1 and θ2 also helps the electrolyte to penetrate into the battery through the included angles θ1 and θ2.

[0120] The tail portion 132 will be further described below with reference to embodiments and comparative examples. The embodiments and comparative examples described below are designed with reference to a common 21 series cylindrical lithium battery.

[0121] Example 2:

[0122] Example 2 provides a cylindrical lithium battery, comprising a casing 110, a cap 120, a positive current collector 130, a core 140, and a negative current collector 150. The positive current collector 130 includes a disk portion 131 and a tail portion 132 connected to each other. The disk portion 131 is connected to the positive terminal 141 of the core 140, and the tail portion 132 is connected to the cap 120. The tail portion 132 has a constant thickness along its length, and at least one pair of fuse grooves 1321 are formed on the tail portion 132. The distance L4 between the center of the fuse groove 1321 and the end of the tail portion 132 away from the disk portion 131 is 72% of the length L3 of the tail portion 132. The minimum cross-sectional area S2 of the tail portion 132 at the fuse groove 1321 is 50% of the overall cross-sectional area S1 of the tail portion 132.

[0123] Comparative Example 3:

[0124] Comparative Example 3 provides a cylindrical lithium battery, which differs from Example 2 in that the minimum cross-sectional area S2 of the tail portion 132 at the fuse groove 1321 is 20% of the overall cross-sectional area S1 of the tail portion 132.

[0125] Comparative Example 4:

[0126] Comparative Example 4 provides a cylindrical lithium battery, which differs from Example 2 in that the minimum cross-sectional area S2 of the tail portion 132 at the fuse groove 1321 is 85% of the overall cross-sectional area S1 of the tail portion 132.

[0127] Comparative Example 5:

[0128] Comparative Example 5 provides a cylindrical lithium battery, which differs from Example 2 in that the distance L4 between the center of the fuse groove 1321 and the end of the tail portion 132 away from the disc portion 131 is 90% of the length L3 of the tail portion 132.

[0129] Table 2 below evaluates the safety protection effect of the positive current collector 130 fabricated in the above embodiments and comparative examples. The specific test method is as follows: The sampled positive current collector 130 is fixed on the fixture of a high-power (rated power 15150W) programmable DC power supply device. The test conditions are set as follows: voltage 20V, current 170A, power 150W, delay time 10s. The temperature sensor is turned on and aimed at the positive current collector 130. The recording function is clicked, and the test is started on the instrument. The experiment ends when the fuse slot 1321 of the positive current collector 130 is observed to be melted. The time and current correlation curves obtained by the device and the melting temperature read by the temperature sensor are recorded.

[0130] Table 2

[0131] As shown in Table 2, when the distance L4 between the center of the fuse groove 1321 and the end of the tail section 132 away from the disc section 131 is 72% of the length L3 of the tail section 132, and the minimum cross-sectional area S2 of the tail section 132 at the fuse groove 1321 is 50% of the total cross-sectional area S1 of the tail section 132, the breaking temperature and melting time of the fuse groove 1321 are relatively reasonable. When the ratio of the minimum cross-sectional area S2 of the tail section 132 at the fuse groove 1321 to the total cross-sectional area S1 of the tail section 132 is too low, the fuse groove 1321 is relatively sensitive to temperature and will melt quickly; conversely, when the ratio of the minimum cross-sectional area S2 of the tail section 132 at the fuse groove 1321 to the total cross-sectional area S1 of the tail section 132 is too high, the sensitivity of the fuse groove 1321 to temperature decreases, and it cannot melt quickly. When the ratio of the distance L4 between the center of the fuse groove 1321 and the end of the tail portion 132 away from the disc portion 131 to the length L3 of the tail portion 132 is too high, the fuse groove 1321 cannot fuse quickly.

[0132] In some embodiments, the positive current collector 130 is made of aluminum. On the one hand, aluminum has the characteristics of low internal resistance and good conductivity. On the other hand, aluminum has a relatively low melting point, so that the fuse groove 1321 can be melted to cut off the current in the event of battery thermal runaway.

[0133] The following is a detailed introduction to core 140.

[0134] The core 140 is formed by winding together positive electrode plates, negative electrode plates, and a separator, as shown in Figure 1. The core 140 is cylindrical in shape, and its diameter D5 is slightly smaller than the inner diameter of the outer shell 110 in order to smoothly pass through the opening 114 into the inner cavity 113 of the outer shell 110. As shown in Figures 1 and 10, after the core 140 is inserted into the shell, it is located in the area defined by the neck 1121 and the bottom 111 of the outer shell 110, that is, in the lower cavity 1132.

[0135] In this embodiment, the core 140 is provided with a positive terminal 141 and a negative terminal 142. The positive terminal 141 is connected to the cap 120 through the positive current collector 130, and the negative terminal 142 is connected to the outer shell 110 through the negative current collector 150.

[0136] To improve the battery's energy density and the welding effect with the positive current collector 130 and negative current collector 150, the positive terminal 141 and negative terminal 142 can be formed by flattening the entire tab. For example, the entire tab foil of the positive and negative current collectors is rotated and flattened by a mechanical conical roller for a certain stroke. Thus, on the one hand, the positive terminal 141 and negative terminal 142 formed by the flattening process are densely stacked, without wasting space in the longitudinal direction. Therefore, the internal space utilization of the casing 110 is high, which can further improve the battery's energy density. On the other hand, the flattened positive electrode structure (i.e., positive terminal 141) and the flattened negative electrode structure (i.e., negative terminal 142) formed by the flattening process have flat cross-sections. They can fit well with the positive current collector 130 and negative current collector 150 respectively, facilitating laser welding and effectively reducing process defects such as incomplete welds.

[0137] In addition, during the winding process, the core 140 forms a through core hole 143 in the middle along the axial direction. The diameter D6 of the core hole 143 needs to be considered to achieve a balance between liquid injection efficiency and weldable area, while ensuring the safety of welding.

[0138] The following is a detailed introduction to the negative electrode collector 150.

[0139] As shown in Figures 1 and 11, the negative electrode current collector 150 is generally circular. Along the thickness direction, the negative electrode current collector 150 has a first side 151 and a second side 152 that are opposite to each other. Since the second side 152 is provided with the raised platform 1521 described below, it is necessary to distinguish the direction when welding the negative electrode current collector 150 to the outer shell 110 and the core 140. Specifically, the second side 152 is welded to the bottom of the shell 111 through the raised platform 1521, and the first side 151 is welded to the negative end 142 of the core 140. Thus, the welding connection between the core 140, the negative electrode current collector 150, and the outer shell 110 is realized, and a passage is formed between the three. That is, the negative electrode current collector 150 indirectly connects the core 140 and the outer shell 110.

[0140] To ensure good contact between the raised platform 1521 and the surface of the housing 110, in this embodiment, the negative electrode current collector 150 is provided with a raised platform 1521 with a flat surface on the second side 152. The surface of the raised platform 1521 protrudes from the surface of the second side 152, and the surface area of ​​the raised platform 1521 is smaller than the surface area of ​​the second side 152. The surface of the raised platform 1521 is suitable for contacting the inner surface of the bottom of the housing 111, and the flatness of the surface of the raised platform 1521 is 0.01-0.05mm. Since the surface of the raised platform 1521 protrudes from the surface of the second side 152, that is, the surface of the raised platform 1521 is the top surface of the second side 152, after the negative electrode current collector 150 is assembled into the housing 110, the surface of the raised platform 1521 will abut against the inner surface of the housing bottom 111. That is, the surface of the raised platform 1521 and the inner surface of the housing bottom 111 are in close contact with each other, forming a surface-to-surface contact connection. Then, the area where the raised platform 1521 overlaps with the housing bottom 111 can be laser-welded through the outer surface of the housing bottom 111, so that the raised platform 1521 is welded to the housing 110. If the flatness of the raised platform 1521 is too large, its fit with the inner surface of the housing bottom 111 will be poor, thus affecting the welding quality; conversely, if the flatness of the raised platform 1521 is too small, it will be difficult to process and the cost will be too high.

[0141] In this embodiment, by setting the ratio of the diameter D7 of the negative electrode current collector 150 to the diameter D5 of the core 140 to 90%-98%, the weldable area between the negative electrode current collector 150 and the core 140 can be effectively increased, resulting in good welding processability. Simultaneously, a smaller raised platform 1521 is provided on the second side 152 of the negative electrode current collector 150. Due to its smaller area, the raised platform 1521 ensures good surface flatness during processing, thereby improving the fit between the surface of the raised platform 1521 and the inner surface of the shell bottom 111. This effectively avoids welding quality problems such as incomplete welds, resulting in batteries using this negative electrode current collector 150 exhibiting better performance and higher yield.

[0142] For ease of processing and cost reduction, in some embodiments, the raised platform 1521 is formed from the negative electrode current collector 150 by a stamping process; that is, the raised platform 1521 and the negative electrode current collector 150 are integrally formed. Therefore, with a reasonable stamping die design, the negative electrode current collector 150 of this embodiment can be processed efficiently, and both the negative electrode current collector 150 and the raised platform 1521 have high dimensional accuracy and good surface quality, facilitating welding with the core 140 and the outer shell 110. Of course, this is not the only possibility; the raised platform 1521 can also be formed in other ways. For example, the raised platform 1521 can be a sheet metal component with excellent weldability and conductivity, which can be bonded to the surface of the second side 152 of the negative electrode current collector 150 by pressing, thereby forming the raised platform 1521.

[0143] In some embodiments, the raised platform 1521 is formed in the central region of the second side 152, thereby enabling the raised platform 1521 to be aligned with the central region of the positive bottom 111 of the housing after the negative current collector 150 is assembled into the housing 110, facilitating the welding of the housing 110 to the raised platform 1521 by a welding device.

[0144] Furthermore, the raised platform 1521 is circular in shape, so that it can be set with the negative electrode current collector 150 at the same center, which facilitates stamping and forming by a stamping die. Of course, the shape of the raised platform 1521 is not limited to circular; for example, the raised platform 1521 can also be square, triangular, or other shapes.

[0145] As shown in Figures 10 and 11, a raised platform 1521 is punched out on the second side 152 of the negative electrode current collector 150 by a stamping process. Correspondingly, a recess 1511 is formed on the first side 151 at the position corresponding to the raised platform 1521. For the purpose of facilitating the welding of the negative electrode current collector 150 and the core 140, in some embodiments, the first side 151 has an annular welding area 1512 around the recess 1511. The surface of the welding area 1512 is adapted to abut against the negative end 142 of the core 140. For example, the welding area 1512 is also configured to have a flat surface so that the surfaces of the two can fit tightly against each other to improve the welding quality.

[0146] As shown in Figure 11, in some embodiments, the diameter of the raised platform 1521 is D8, satisfying D8 / D7 = 28%-38%. As mentioned earlier, the diameter D7 of the negative electrode current collector 150 is approximately the same as the diameter of the core 140. If the diameter of the raised platform 1521 is too large, its surface flatness will be poor, and its fit with the inner surface of the shell bottom 111 will be poor, thus affecting the welding quality. Conversely, if the diameter of the raised platform 1521 is too small, the weldable area of ​​the raised platform 1521 will be small, making it easy to detach during welding, which will increase the difficulty of subsequent welding processes and lead to increased costs.

[0147] Further, as shown in Figure 12, in some embodiments, the height difference between the surface of the raised platform 1521 and the surface of the second side 152 is H4, and the thickness of the negative electrode current collector 150 is T4, satisfying: H4 / T4 = 18%-30%. If the raised platform 1521 is set too high, that is, H4 / T4 is too large, the core 140 will squeeze and deform the periphery of the negative electrode current collector 150 during assembly, and will also occupy additional longitudinal space of the battery; conversely, if the raised platform 1521 is set too low, that is, H4 / T4 is too small, the raised platform 1521 is difficult to process, for example, it is difficult to form the raised platform 1521 by stamping process.

[0148] The negative electrode current collector 150 will be further described below with reference to the embodiments and comparative examples. The embodiments and comparative examples described below are designed with reference to a common 21 series cylindrical lithium battery.

[0149] Example 3:

[0150] Example 3 provides a cylindrical lithium battery, comprising a casing 110, a cap 120, a positive current collector 130, a core 140, and a negative current collector 150. The negative current collector 150 has a diameter of 18 mm, with a raised platform 1521 punched out on its second side 152. Correspondingly, a recess 1511 is formed on the first side 151 at a position corresponding to the raised platform 1521. Around the recess 1511, the first side 151 has an annular welding area 1512. The surface of the welding area 1512 is connected to the negative terminal 142 of the core 140 via laser through-welding. The diameter D8 of the raised platform 1521 is 35% of the diameter D7 of the negative current collector 150, and the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is 25% of the thickness T4 of the negative current collector 150.

[0151] Comparative Example 6:

[0152] Comparative Example 6 provides a cylindrical lithium battery, which differs from Example 3 in that: the diameter D8 of the raised platform 1521 is 35% of the diameter D7 of the negative electrode current collector 150, and the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is 60% of the thickness T4 of the negative electrode current collector 150.

[0153] Comparative Example 7:

[0154] Comparative Example 7 provides a cylindrical lithium battery that differs from Example 3 in that the diameter D8 of the raised platform 1521 is 60% of the diameter D7 of the negative electrode current collector 150, and the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is 25% of the thickness T4 of the negative electrode current collector 150.

[0155] Comparative Example 8:

[0156] Comparative Example 8 provides a cylindrical lithium battery, which differs from Example 3 in that: the diameter D8 of the raised platform 1521 is 10% of the diameter D7 of the negative electrode current collector 150, and the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is 25% of the thickness T4 of the negative electrode current collector 150.

[0157] Table 3 below evaluates the welding and assembly effects of the negative current collector 150 fabricated in the above embodiments and comparative examples. The specific testing method is as follows: The sampled negative current collector 150 is welded to the core 140 and installed into the outer shell 110, so that the shell 111 fits against the raised platform 1521. Laser penetration welding is used to weld the shell bottom 111 to the negative current collector 150 at the bottom of the shell. A cutter is used to cut the shell 110 3mm from the bottom along the diameter direction. The shape of the negative current collector 150 is visually observed. Then, four small edges of the negative current collector 150 are clamped using diagonal pliers. A tensile testing machine is used to clamp the four edges and pull them apart. The maximum pulling force required to separate the negative current collector 150 from the shell 110 is read and recorded. The remaining portion of the negative current collector 150 on the shell bottom 111 is drawn using a microscope, and the remaining area is measured and recorded. The weld mark status of the remaining portion is also visually observed.

[0158] Table 3

[0159] As shown in Table 3, when the diameter D8 of the raised platform 1521 is 35% of the diameter D7 of the negative current collector 150, and the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is 25% of the thickness T4 of the negative current collector 150, the negative current collector 150 has good overall rigidity and can resist deformation during assembly. Furthermore, the raised platform 1521 can also fit well with the inner surface of the shell bottom 111, and the welding quality between the two is good, with no welding defects such as incomplete welds or burn-throughs found. The connection strength between the two is also relatively ideal. When the height difference H4 between the surface of the raised platform 1521 and the surface of the second side 152 is large, the negative current collector 150 deforms after assembly, and there are welding defects such as incomplete welds between it and the shell bottom 111, resulting in low connection strength. When the diameter of the raised platform 1521 is too large, the negative current collector 150 deforms after assembly. Although the connection strength between the negative current collector 150 and the shell bottom 111 is relatively large, there is a welding defect of weld penetration between the two. When the area of ​​the raised platform 1521 is too small, the negative current collector 150 deforms after assembly, and there is a welding defect of incomplete welding between it and the shell bottom 111, resulting in poor connection strength between the two.

[0160] In some embodiments, the negative current collector 150 is made of copper, and its surface is plated with a nickel layer. Compared to a negative current collector 150 made of copper-nickel alloy, using copper as the substrate has the characteristic of extremely low internal resistance. At the same time, by plating a nickel layer on the surface of the negative current collector 150, the corrosion resistance of the negative current collector 150 can be effectively improved.

[0161] Furthermore, the thickness of the nickel layer is set to 0.08-1.5μm, more preferably 0.9-1.1μm. If the nickel layer thickness is too small, it cannot play a role in preventing oxidation; conversely, if the nickel layer thickness is too large, on the one hand, it increases the difficulty of the nickel plating process and the cost, and on the other hand, it increases the hardness of the negative electrode current collector 150, resulting in a decrease in the plasticity of the negative electrode current collector 150, and also increases the internal resistance, leading to a decrease in battery performance.

[0162] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this implementation. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0163] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A cylindrical lithium battery, comprising a shell (110), a cap (120), a positive current collector (130), a roll core (140) and a negative current collector (150), a positive end (141) of the roll core (140) is connected with the cap (120) through the positive current collector (130), and a negative end (142) of the roll core (140) is connected with the shell (110) through the negative current collector (150) ; The positive current collector (130) comprises a disc body (131) and a tail body (132) connected with each other, the disc body (131) is connected with the positive end (141), the tail body (132) is connected with the cap (120), a circular first hole (1315) is arranged in the center of the disc body (131), at least one circular second hole (1316) is arranged on the periphery of the first hole (1315), and the sum of the areas of all the second holes (1316) is 0.9-1.5 times the area of the first hole (1315) ; at least one fuse slot (1321) is arranged on the tail body (132), the tail body (132) has an overall cross-sectional area S1 except the position of the fuse slot (1321), the tail body (132) has a minimum cross-sectional area S2 at the position of the fuse slot (1321), and the minimum cross-sectional area S2 is 45%-65% of the overall cross-sectional area S1; The negative current collector (150) has opposite first and second sides (151 and 152), the first side (151) is connected with the negative end (142), and a circular and flat-surfaced raised platform (1521) is arranged in the center of the second side (152), the raised platform (1521) is connected with the shell (110), the diameter D8 of the raised platform (1521) is 28%-38% of the diameter D7 of the negative current collector (150), and the height difference H4 between the surface of the raised platform (1521) and the surface of the first side (151) is 18%-30% of the thickness T4 of the negative current collector (150).

2. The cylindrical lithium battery of claim 1, wherein, The roll core (140) has a roll core hole (143), the diameter D3 of the first hole (1315) is 1.4-1.8 times the diameter D6 of the roll core hole (143), and the diameter D4 of the second hole (1316) is 50%-70% of the diameter D3 of the first hole (1315) ; the flatness of the surface of the raised platform (1521) is 0.01-0.05 mm.

3. The cylindrical lithium battery according to claim 1 or 2, wherein, The positive end (141) and the negative end (142) are formed by full-tab rubbing, one side of the disc body (131) facing the positive end (141) abuts against the positive end (141) formed by full-tab rubbing, and the first side (151) of the negative current collector (150) abuts against the negative end (142) formed by rubbing.

4. The cylindrical lithium battery of claim 3, wherein, The diameter D2 of the disk body (131) is 80%-95% of the diameter D5 of the core (140); the diameter D7 of the negative electrode current collector (150) is 90%-98% of the diameter D5 of the core (140).

5. The cylindrical lithium battery according to any one of claims 1 to 4, wherein, The disc body (131) is a closed axisymmetric shape formed by connecting the first side (1311), the arc (1312), the second side (1313), and the third side (1314) end to end. The tail body (132) is a closed axisymmetric shape formed by connecting the third side (1314), the fifth side (1322) extending along the length of the tail body (132), the fourth side (1324) away from the disc body, and the sixth side (1323) extending along the length of the tail body (132), end to end. The two ends of the fifth side are connected to the fourth side (1314) and the arc (1312). 24) is connected to the first side (1311), and the two ends of the sixth side (1323) are connected to the fourth side (1324) and the second side (1313) respectively; the raised platform (1521) is integrally formed by stamping the negative electrode current collector (150), and a recess (1511) is formed on the first side (151) at the position corresponding to the raised platform (1521). Around the recess (1511), a welding area (1512) is formed on the first side (151), and the surface of the welding area (1512) abuts against the negative electrode (142) formed by flattening.

6. The cylindrical lithium battery of claim 5, wherein, The positive current collector (130) is made of aluminum, the negative current collector (150) is made of copper, and the surface of the negative current collector (150) is plated with a nickel layer.

7. The cylindrical lithium battery of claim 6, wherein, The thickness of the nickel layer is 0.08-1.5 μm.

8. The cylindrical lithium battery of any one of claims 5 to 7, wherein, The first width W1 of the tail body (132) is D2*sin(∠B / 2), and 20°≤∠B≤40°, where ∠B takes the center of the circle corresponding to the arc (1312) as its vertex, and the two sides pass through the intersection points of the fifth side (1322) and the sixth side (1323) with the whole circle containing the arc (1312).

9. The cylindrical lithium battery of claim 8, wherein, The second width W2 of the tail portion (132) at the fuse groove (1321) is 3 / 8 to 3 / 4 of the first width W1 of the tail portion (132).

10. The cylindrical lithium battery according to any one of claims 5 to 9, wherein, The disc body (131) has a central angle A, and 40°≤∠A≤60°; wherein, the central angle A has the center of the circle corresponding to the arc (1312) as its vertex, and the two sides pass through the endpoints of the first side (1311) away from the arc (1312) and the second side (1313) away from the arc (1312), respectively.

11. The cylindrical lithium battery according to any one of claims 5 to 10, wherein, The angle θ1 between the fifth side (1322) and the first side (1311) is 45-90°, and the angle θ2 between the sixth side (1323) and the second side (1313) is 45-90°.

12. The cylindrical lithium battery of any one of claims 1 to 11, wherein, The length L3 of the tail section (132) is 85%-95% of the diameter D2 of the disc section (131).

13. The cylindrical lithium battery of any one of claims 1 to 12, wherein, The outer shell (110) includes a bottom (111) and a side wall (112). The top of the side wall (112) has an opening (114). The side wall (112) is circumferentially concave near the opening (114) to form a neck (1121). The neck (1121) includes a first wall portion (1121a) and a second wall portion (1121b) extending toward the center of the outer shell (110). The neck (1121) also includes a connecting portion (1121c) for connecting the first wall portion (1121a) and the second wall portion (1121b). The outer surfaces of the first wall portion (1121a), the second wall portion (1121b) and the connecting portion (1121c) together define a necking groove (1123). The first wall portion (1121a) and the second wall portion (1121b) are both inclined at a certain angle to the bottom (111).

14. The cylindrical lithium battery of claim 13, wherein, The raised platform (1521) is connected to the inner surface of the shell bottom (111).

15. The cylindrical lithium battery according to claim 13 or 14, wherein, Let α be the larger of the angle between the first wall portion (1121a) and the shell bottom (111) and the angle between the second wall portion (1121b) and the shell bottom (111), and satisfy: α < 10°.

16. The cylindrical lithium battery of claim 15, wherein, The included angle α satisfies: 1° < α < 5°.

17. The cylindrical lithium battery of any one of claims 13-16, wherein, The dimension L5 of the fuse groove (1321) along the length direction of the tail portion (132) is 0 < L5 ≤ W1, where W1 is the first width of the tail portion (132); the depth H3 of the necking groove (1123) in the radial direction is 5%-10% of the outer diameter D1 of the outer shell (110).

18. The cylindrical lithium battery of claim 17, wherein, The dimension L5 of the fuse groove (1321) along the length direction of the tail body (132) is 1 / 4 to 3 / 4 of the first width W1 of the tail body (132); the minimum wall thickness T2 of the neck (1121) is 0.1-0.2 mm, and the minimum wall thickness T2 of the neck (1121) is more than 80% of the wall thickness T1 of the side wall (112).

19. The cylindrical lithium battery of any one of claims 13-18, wherein, The distance L1 from the lowest point of the constricted neck (1121) to the upper surface of the shell bottom (111) is 90%-98% of the height H1 of the outer shell (110), and the height H2 of the constricted groove (1123) is 0.1%-1% of the height H1 of the outer shell (110).

20. The cylindrical lithium battery of any one of claims 1 to 19, wherein, The distance L4 between the center of the fuse groove (1321) and the end of the tail section (132) away from the disc section (131) is 68%-78% of the length L3 of the tail section (132).

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