Soft package cylindrical battery and preparation method thereof

Abstract

The invention discloses a soft package cylindrical battery and a preparation method thereof, the soft package cylindrical battery comprises a battery cell and a support column, the diameter of the battery cell is not more than 18.5 mm, the battery cell is provided with a support hole, and the support column is arranged in the support hole; the ratio of the diameter of the supporting hole to the diameter of the supporting column is 1: (0.75-0.95); the supporting column is made of an insulating material, and the insulating material comprises any one of polypropylene and polyethylene. Due to the fact that the supporting hole is formed in the battery cell, and the supporting column is arranged in the supporting hole, when the soft package cylindrical battery is extruded or impacted, the supporting column can bear pressure, the battery cell is prevented from excessively collapsing, and the stability and safety of the structure of the soft package cylindrical battery are improved. Moreover, the supporting columns and the supporting holes are in clearance fit, so that when the soft package cylindrical battery is extruded along the radial direction, the gaps between the supporting columns and the supporting holes can provide a deformation space for the deformation of the battery cell, the pole pieces of the battery cell are prevented from being broken in the extrusion process, and the stability and the safety of the soft package cylindrical battery structure are further improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a soft-package cylindrical battery and a preparation method thereof. Background Art

[0002] As the demand for portability and functionality of mobile electronic devices grows, the demand for miniaturized, high-energy-density lithium-ion batteries also increases. In particular, in the fields of digital products, power tools, and power toys, the demand for small-diameter, high-capacity soft-pack cylindrical batteries (diameter less than 18.5mm and capacity over 200mAh) has risen sharply.

[0003] However, although the soft-pack materials of such batteries can provide a certain degree of flexibility, they show obvious deficiencies in terms of extrusion resistance and impact resistance when subjected to large external forces. To address this problem, the prior art uses high-strength copper-aluminum foil and diaphragms with high puncture strength to enhance the stability of the physical structure. However, these methods not only increase manufacturing costs, but may also sacrifice energy density, and fail to fully solve the safety issues that may arise when the battery is subjected to extreme external forces. Summary of the invention

[0004] The embodiment of the present invention provides a soft-pack cylindrical battery and a preparation method thereof, so as to solve the problem that the existing soft-pack cylindrical battery has poor extrusion resistance and impact resistance, and improve the stability and safety of the soft-pack cylindrical battery structure.

[0005] Specifically, the present invention provides a soft-pack cylindrical battery, comprising a battery cell and a support column, wherein the diameter of the battery cell does not exceed 18.5 mm, the battery cell is provided with a support hole coaxial with the battery cell, the support column is arranged in the support hole, and the ratio of the diameter of the support hole to the diameter of the support column is 1:(0.75-0.95); the support column is an elastically deformable structural member, and the support column is made of insulating material, and the insulating material includes any one of polypropylene and polyethylene.

[0006] Optionally, the ratio of the diameter of the support hole to the diameter of the support column is 1:(0.9-0.95).

[0007] Optionally, a difference X between a diameter of the support hole and a diameter of the support column satisfies: 0.15≤X≤0.8.

[0008] Optionally, the elastic deformation E of the support column satisfies: 20%≤E≤50%.

[0009] Optionally, the support column is a solid columnar structure; Alternatively, the support column is provided with a fixing hole extending along its axial direction, and a reinforcing column is fixedly arranged in the fixing hole.

[0010] Optionally, the reinforcement column is made of metal material.

[0011] Optionally, the diameter of the supporting hole is 3.0 mm to 3.5 mm.

[0012] Optionally, the soft-pack cylindrical battery further includes a shell, and the battery cell and the support column are arranged in the shell.

[0013] The present invention also provides a method for preparing a soft-package cylindrical battery, comprising the following steps: Winding a plurality of layers of a negative electrode sheet, a separator, and a positive electrode sheet stacked in sequence to form a battery core, wherein a support hole is hinged at the center of the battery core; A support column having a diameter smaller than that of the support hole is inserted into the support hole to obtain the soft-package cylindrical battery.

[0014] The beneficial effects of the present invention are: In the soft-pack cylindrical battery and the preparation method thereof provided by the present invention, a support hole is provided in the battery cell, and a support column is provided in the support hole, so that when the soft-pack cylindrical battery is squeezed or impacted, the support column can bear the pressure to prevent the battery cell from collapsing, thereby improving the stability and safety of the soft-pack cylindrical battery structure.

[0015] Furthermore, due to the clearance between the support column and the support hole, on the one hand, when the soft-pack cylindrical battery is squeezed along its radial direction, the gap between the support column and the support hole can provide deformation space for the deformation of the battery cell, thereby preventing the battery cell's pole piece from breaking during the squeezing process, and further improving the stability and safety of the soft-pack cylindrical battery structure. On the other hand, it can provide buffering when the battery cell's pole piece expands, thereby preventing stress concentration from causing the pole piece to fall off and causing lithium precipitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0017] Figure 1 is a schematic structural diagram of a soft-pack cylindrical battery in one embodiment of the present invention; Figure 2 It is a schematic structural diagram of a support column in one embodiment of the present invention.

[0018] In the figure: 100, battery cell, 110, support hole, 200, support column, 210, fixing hole, 300, reinforcement column. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In the existing technology, soft-pack cylindrical batteries with a diameter of no more than 18.5 mm and a capacity greater than 200 mAh have shown unique advantages in efficient energy storage in a limited space. This type of lithium battery can store more electrical energy in a smaller volume, so it is often used in small devices such as portable medical devices and wireless sensors that require long-term power supply. However, these small devices are often carried in daily use, which makes them more likely to face collision risks. The external packaging material of soft-pack cylindrical batteries is relatively soft, so they become particularly fragile when squeezed or impacted.

[0023] Based on this, the inventor creatively proposed to provide a support column in the battery cell that matches the gap of the battery cell to improve the stability and safety of the soft-pack cylindrical battery structure. Specifically: Figure 1 is a schematic structural diagram of a soft-pack cylindrical battery in one embodiment of the present invention, such as Figure 1 As shown, and refer to Figure 2An embodiment of the present invention provides a soft-pack cylindrical battery, including a battery cell 100 and a support column 200, wherein the diameter of the battery cell 100 does not exceed 16 mm, and the battery cell 100 is provided with a support hole 110 coaxial with the battery cell 100, and the support column 200 is arranged in the support hole 110, and the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is 1:(0.75-0.95); the support column 200 is an elastically deformable structural member, and the support column 200 is made of an insulating material, and the insulating material includes any one of polypropylene and polyethylene.

[0024] In the embodiment of the present invention, since a support hole 110 is provided in the battery cell 100, and a support column 200 is provided in the support hole 110, when the soft-pack cylindrical battery is squeezed or impacted, the support column 200 can bear the pressure, prevent the battery cell 100 from collapsing, and improve the stability and safety of the soft-pack cylindrical battery structure. In addition, since the support column 200 and the support hole 110 are clearance-matched, on the one hand, when the soft-pack cylindrical battery is squeezed along its radial direction, the gap between the support column 200 and the support hole 110 can provide deformation space for the deformation of the battery cell 100, avoid the rupture of the pole piece of the battery cell 100 during the squeezing process, and further improve the stability and safety of the soft-pack cylindrical battery structure. On the other hand, buffering can be performed when the pole piece of the battery cell 100 expands, avoiding stress concentration that causes the pole piece to fall off and trigger lithium precipitation.

[0025] Furthermore, since the support column 200 is an elastically deformable structural member, it can effectively support the battery cell 100 when the soft-pack cylindrical battery is squeezed, completely preventing the positive / negative electrode sheets from breaking during the squeezing process, and further improving the structural performance and safety performance of the battery.

[0026] Furthermore, if the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is too small, the gap between the support column 200 and the support hole 110 is too small, and it is difficult to provide sufficient deformation space for the deformation of the battery cell 100, which is not conducive to protecting the electrode from being damaged during the extrusion process. At the same time, due to the small gap between the support column and the support hole, the support column will cause a certain proportion of the inner circle electrode of the battery cell to be interfered by the support column during the insertion process, resulting in the scrapping of the battery cell, and the yield rate of the process of inserting the support column will be very low. If the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is too large, the gap between the support column 200 and the support hole 110 is too large. When the soft-pack cylindrical battery is squeezed along its radial direction, excessive deformation is required to make the side wall of the support hole 110 contact with the support column 200 and transmit the extrusion force to the support column 200. Therefore, it is impossible to support the battery cell 100 in time and it is difficult to prevent the battery cell 100 from excessive collapse.

[0027] In one embodiment of the present invention, the insulating material includes any one of polypropylene (PP) and polyethylene (PE), which are resistant to electrolyte corrosion, high temperature resistance of 150 degrees under vacuum conditions, and high strength, and thus can provide stable support for the battery cell 100.

[0028] Preferably, the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is 1:(0.9-0.95). Specifically, the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is 1:0.90, 1:0.91, 1:0.92, 1:0.93, 1:0.94 or 1:0.95.

[0029] In an alternative embodiment of the present invention, the diameter of the support hole 110 is 3.0 mm to 3.5 mm. Specifically, the diameter of the support hole 110 is 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm or 3.5 mm. The difference X between the diameter of the support hole 110 and the diameter of the support column 200 satisfies: 0.15≤X≤0.8. If the difference X between the diameter of the support hole 110 and the diameter of the support column 200 is too small, it is difficult to provide sufficient deformation space for the deformation of the battery cell 100, which is not conducive to protecting the electrode from being damaged during the extrusion process. At the same time, the battery cell process yield will also be reduced. If the difference X between the diameter of the support hole 110 and the diameter of the support column 200 is too large, when the soft-pack cylindrical battery is squeezed in the radial direction, excessive deformation is required to make the side wall of the support hole 110 contact the support column 200, and the squeezing force is transmitted to the support column 200, so that the battery cell 100 cannot be supported in time, and it is difficult to prevent the battery cell 100 from collapsing. Specifically, the difference X between the diameter of the support hole 110 and the diameter of the support column 200 is 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8.

[0030] In one embodiment of the present invention, the elastic deformation E of the support column 200 satisfies: 20%≤E≤50%. If the elastic deformation E is small, the elastic deformation of the support column 200 is small, and it cannot provide sufficient buffering effect for the pole piece when the battery cell 100 is squeezed, which easily causes the pole piece to fall off or break; if the elastic deformation E is large, the elastic deformation of the support column 200 is large, and it cannot provide support for the battery cell 100, and it is difficult to prevent the battery cell 100 from excessively collapsing.

[0031] During gravity impact, a heavy object falls from a height, and the potential energy of the heavy object is converted into kinetic energy and applied to the soft-pack cylindrical battery, and impacts the support column 200, which can easily cause the support column 200 to deform and break, and easily damage the positive and negative electrodes; in severe cases, the broken tip of the support column 200 will also insert into the battery cell, and contact the positive and negative electrodes at the same time, causing an internal short circuit in the battery cell 100. For this reason, in one embodiment of the present invention, the support column 200 is a solid columnar structural member, and the support column 200 is made of insulating material to prevent the support column 200 from electrically connecting the innermost positive electrode sheet and the negative electrode sheet of the battery cell 100 when the heavy object impacts, causing an internal short circuit.

[0032] like Figure 2 As shown, in an alternative embodiment of the present invention, the support column 200 is provided with a fixing hole 210 extending along its axial direction, and a reinforcing column 300 is fixedly arranged in the fixing hole 210. The support column 200 is made of an insulating material, and the insulating material includes any one of polypropylene and polyethylene; the reinforcing column 300 is made of a metal material. Since the metal reinforcing column 300 is arranged in the support column 200, it can provide support for the soft-pack cylindrical battery in the axial and radial directions, and prevent the pole piece from being damaged when impacted by a heavy object. Specifically, the metal material includes steel, aluminum, copper, stainless steel or aluminum alloy, and the diameter of the reinforcing column 300 is 1.2mm-1.5mm. If the diameter of the reinforcing column 300 is too large, the wall thickness of the outer support column 200 is smaller, that is, the elastic material layer is thinner, and it cannot provide a buffering effect for the electrode when the battery cell 100 is squeezed, which may easily cause the electrode to fall off or break; if the diameter of the reinforcing column 300 is too small, the reinforcing column 300 is easy to bend, and it is difficult to provide support for the battery cell 100, so it is difficult to avoid damage to the electrode when it is impacted by heavy objects.

[0033] In one embodiment of the present invention, the soft-pack cylindrical battery also includes an outer shell, and the battery cell 100 and the support column 200 are arranged in the outer shell, so that when gravity impacts, the support column can consume part of the impact force, and the positive and negative electrodes in the innermost circle of the battery cell will not have an internal short circuit, and ultimately a large proportion of them can pass the heavy object impact test.

[0034] The present invention also provides a method for preparing a soft-package cylindrical battery, comprising the following steps: Winding up the negative electrode sheet, the separator, and the positive electrode sheet stacked in sequence to form a plurality of coaxially arranged battery cells, wherein a support hole is hinged at the center of the battery cell; A support column 200 having a diameter smaller than that of the support hole 110 is inserted into the support hole 110 to obtain the soft-pack cylindrical battery.

[0035] Since the reaming process has high precision, the support hole can be enlarged by the reaming process, which can ensure that the diameter of the support hole 110 meets the requirements and avoid the hole diameter being too large or too small.

[0036] The present invention is further described below by way of examples. However, the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0037] Example 1 A soft-pack cylindrical battery includes a battery cell 100 and a support column 200. The diameter of the battery cell 100 is 15 mm. The battery cell 100 is provided with a support hole 110 coaxial with the battery cell 100, and the diameter of the support hole 110 is 3.0 mm. The support column 200 is arranged in the support hole 110, and the diameter of the support column 200 is 2.5 mm. The support column 200 is made of PP. The ratio Y of the diameter of the support hole 110 to the diameter of the support column 200 is 1:0.83.

[0038] The differences between Examples 2-9 and Comparative Examples 1-3 and Example 1 are shown in Table 1.

[0039] Example 10 A soft-pack cylindrical battery includes a battery cell 100 and a support column 200. The diameter of the battery cell 100 is 15 mm. The battery cell 100 is provided with a support hole 110 coaxial with the battery cell 100, and the diameter of the support hole 110 is 3.0 mm. The support column 200 is arranged in the support hole 110, and the diameter of the support column 200 is 2.5 mm. The support column 200 is made of PP. The ratio Y of the diameter of the support hole 110 to the diameter of the support column 200 is 1:0.83. The support column 200 is provided with a fixing hole 210 extending along its axial direction, and a reinforcing column 300 is transitionally fitted in the fixing hole 210, and the diameter of the reinforcing column 300 is 1.5 mm. The reinforcing column 300 is made of copper.

[0040] The differences between Examples 11 to 13 and Example 10 are shown in Table 1.

[0041] Table 1 Condition variables of Examples 1-13 and Comparative Examples 1-3

[0042] When assembling the soft-pack cylindrical battery, if the support column 200 cannot be inserted into the battery cell 100, or interferes with the electrode when inserting the battery cell, causing the battery cell to be scrapped, it is considered as poor assembly, and the proportion of good assembly (assembly yield) in each embodiment and comparative example is counted.

[0043] The soft-pack cylindrical batteries of Examples 1 to 13 and Comparative Examples 1 to 3 were tested as follows, and the test results are shown in Table 2; 1. Extrusion test After the soft-pack cylindrical battery is fully charged according to the standard method of 0.2C, the soft-pack cylindrical battery is placed between two flat plates, with the axis of the soft-pack cylindrical battery parallel to the two flat plates.

[0044] Extrusion is performed perpendicular to the flat plate: an extrusion force of 13±0.78 kN is applied between the flat plates, and the extrusion speed is 0.1 mm / s. Once the pressure reaches the maximum value or the voltage of the soft-pack cylindrical battery drops by one third, the extrusion test can be stopped; during the extrusion process, the time interval between the extrusion reaching the cutoff condition and the extrusion device stopping is no more than 100 ms. For each embodiment and comparative example, 15 well-assembled batteries are tested. During the test, if the soft-pack cylindrical battery does not catch fire or explode, the test is passed.

[0045] 2. Heavy object impact test After fully charging the soft-pack cylindrical battery at 0.2C, place it on the platform surface, with the axis of the soft-pack cylindrical battery parallel to the platform, and place a metal rod with a diameter of 15.8mm±0.2mm horizontally on the upper surface of the geometric center of the soft-pack cylindrical battery. A weight with a mass of 9.1kg±0.1kg is dropped freely from a height of 610mm±25mm to hit the battery surface with the metal rod, and observe for 6 hours. 15 well-assembled batteries are tested for each embodiment and comparative example. During the test, if the soft-pack cylindrical battery does not catch fire or explode, the test is passed.

[0046] Table 2 Test results of Examples 1-13 and Comparative Examples 1-3

[0047] During assembly, the soft-pack cylindrical battery cell is soft in texture and easily deformed; as in Example 5, the ratio of the diameter of the support hole 110 to the diameter of the support column 200 is too large, which may easily cause interference between the battery cell 100 and the support column 200, and the support column 200 may not be inserted into the battery cell 100, or may interfere with the electrode when inserted into the battery cell 100, resulting in the battery cell being scrapped, the assembly yield being low, and mass production being impossible.

[0048] It can be seen from Table 2 that Example 4 is the optimal example. In the extrusion test, the battery cells 100 of each embodiment are gap-fitted with support columns 200, and the support columns 200 can withstand pressure during extrusion, so 15 batteries of each embodiment have passed the extrusion test. The support columns 200 in Comparative Example 1 are made of phenolic resin, which is relatively hard. Therefore, when the battery cell 100 is extruded, it cannot provide a buffer for the pole piece, which can easily cause the pole piece to fall off or break, resulting in a lower pass rate. The battery cells 100 in Comparative Examples 2 and 3 are provided with support holes 110, but no support columns 200 are provided, so that the entire battery cell has a cylindrical structure, which is directly flattened during extrusion, and the innermost circle of the pole piece is easy to break, so the pass rate is low. Although the battery cell 100 of Example 5 is provided with a support column 200, the gap between the wall of the support hole 110 and the support column 200 is small, and it is difficult to provide sufficient deformation space for the battery cell 100, resulting in a reduced pass rate. At the same time, due to the small difference between the support column and the support hole, the support column and the inner circle positive and negative plates are easily interfered during the rod insertion process, resulting in a low yield of the finished product of this process.

[0049] In the heavy object impact test, the ratio of the diameter of the support hole 110 to the diameter of the support column 200 in Example 4 is moderate, so the pass rate of the test is the highest. In Example 1 and Example 3, the support column 200 is too thin, and the impact of heavy objects can easily cause the support column 200 to deform and break, thereby damaging the positive and negative electrodes. In severe cases, it can cause the battery cell to break into two parts, reducing its pass rate. In Example 5, the gap between the support column 200 and the support hole 110 is too small. During the insertion of the support column 200, it is very easy for the support column 200 and the inner circle positive and negative electrodes to interfere with each other, resulting in a low yield of the finished product of this process. In Example 6 and Example 7, the ratio of the diameter of the pole support hole 110 to the diameter of the support column 200 is reduced relative to Example 4. Excessive deformation is required to make the side wall of the support hole 110 contact with the support column 200 and transfer the extrusion force to the support column 200. Therefore, it is impossible to support the battery cell 100 in time, and it is difficult to prevent the battery cell 100 from collapsing, so the pass rate is reduced. Compared with Example 4, Example 8, or Example 9 compared with Example 6, the material of the support column 200 is changed, so its pass rate is affected to a certain extent. In Examples 10 to 13, a metal reinforcement column is provided in the support column 200, which increases the mechanical strength of the support column 200, which is beneficial to improve the impact of the battery cell 100 in the axial direction, but reduces the elastic modulus of the support column 200, so the pass rate of heavy object impact is reduced. In Comparative Example 1, the support column 200 is made of phenolic resin, which is brittle and fragile, and cannot provide support, and the broken fragments can easily penetrate into the positive and negative electrodes, so it cannot pass the test. Comparative Examples 2 and 3 do not have support columns 200, so they lack support and cannot pass the test.

[0050] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A soft-pack cylindrical battery, characterized in that: It includes a battery cell and a support column, the diameter of the battery cell does not exceed 18.5 mm, the battery cell is provided with a support hole coaxial with the battery cell, the support column is arranged in the support hole, and the ratio of the diameter of the support hole to the diameter of the support column is 1:(0.75-0.95); the support column is an elastically deformable structural member, the support column is made of insulating material, and the insulating material includes any one of polypropylene and polyethylene.

2. The soft-pack cylindrical battery according to claim 1, characterized in that: The ratio of the diameter of the support hole to the diameter of the support column is 1:(0.9-0.95).

3. The soft-pack cylindrical battery according to claim 1, characterized in that: A difference X between the diameter of the support hole and the diameter of the support column satisfies: 0.15 mm≤X≤0.8 mm.

4. The soft-pack cylindrical battery according to claim 1, characterized in that: The elastic deformation amount E of the support column satisfies: 20%≤E≤50%.

5. The soft-pack cylindrical battery according to claim 1, characterized in that: The support column is a solid columnar structural member; Alternatively, the support column is provided with a fixing hole extending along its axial direction, and a reinforcing column is fixedly arranged in the fixing hole.

6. The soft-pack cylindrical battery according to claim 5, characterized in that: The reinforcement column is made of metal material.

7. The soft-pack cylindrical battery according to claim 1, characterized in that: The diameter of the supporting hole is 3.0 mm to 3.5 mm.

8. The soft-pack cylindrical battery according to claim 1, characterized in that: The soft-pack cylindrical battery also includes a shell, and the battery cell and the support column are arranged in the shell.

9. A method for preparing a soft-package cylindrical battery according to any one of claims 1 to 8, characterized in that: The following steps are involved: Winding a plurality of layers of a negative electrode sheet, a separator, and a positive electrode sheet stacked in sequence to form a battery core, wherein a support hole is hinged at the center of the battery core; A support column having a diameter smaller than that of the support hole is inserted into the support hole to obtain the soft-package cylindrical battery.

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