Patent Application
20110217571
1. Technical Field
One or more embodiments of the present invention relate to a battery pack and a method of manufacturing the same, and more particularly, to a battery pack including a tapping screw and a method of manufacturing the battery pack.
2. Related Art
Recently, compact and light portable electric/electronic devices, such as cellular phones, notebook computers, camcorders, etc., are being actively developed and produced. Accordingly, portable electric/electronic devices include battery packs so that they can be operated even in places where additional power sources are not available. Battery packs often employ economical secondary batteries capable of charging and discharging. Representative secondary batteries include a nickel (Ni)-cadmium (Cd) battery, a Ni-MH battery, a lithium (Li) battery, a Li-ion secondary battery, etc. The operating voltage of the lithium ion secondary battery is about three times higher than that of the Ni—Cd battery or the Ni-MH battery, which are usually used as a power source of portable electronic devices. Also, the Li-ion secondary battery is widely used in view of high energy density per unit weight. Secondary batteries generally use lithium-based oxides as positive electrode active materials and carbon-based materials as negative electrode active materials. In general, a secondary battery may be a liquid electrolyte battery or a polymer electrolyte battery according to the type of electrolyte in the secondary battery. In this instance, a Li battery using a liquid electrolyte is referred to as a Li-ion battery, and a Li battery using a polymer electrolyte is referred to as a lithium polymer battery.
A secondary battery includes a bare cell that is formed by sealing a can accommodating an electrode assembly and an electrolyte, and a protection circuit substrate electrically connected to the bare cell. The bare cell charges/discharges electricity via a chemical reaction. The protection circuit substrate controls charging/discharging of the bare cell and prevents overcharging/overdischarging of the bare cell to protect the bare cell.
When the bare cell and the protection circuit are connected to form the secondary battery, electrical resistance therebetween should be reduced in order to improve charging/discharging efficiency. More specifically, if the electrical resistance between the bare cell and the protection circuit module is great, the charging/discharging efficiency of the bare cell is reduced.
Secondary batteries may go through a reliability test for determining whether the secondary battery is stable enough to withstand impacts. These impacts include those caused when the secondary battery is mounted in an electronic product by integrally connecting the bare cell and the protection circuit substrate. If there is an external impact, the electrical resistance between the bare cell and the protection circuit substrate is increased. The electrical resistance increases as contact resistance increases where the bare cell and the protection circuit substrate are connected.
The aforementioned needs are satisfied by the present invention which in one embodiment comprises a battery pack comprising a bare cell having an electrode assembly and a cap plate, a protection circuit module positioned on top of the cap plate and a cover that is positioned over the protection circuit module. In this embodiment the battery back also includes at least one threaded connector that engages with the cover and the protection circuit module and is secured into the cap plate so as to secure the cover and the protection circuit module to the cap plate. In this embodiment, the threads of the at least one connector are polished and the polished threads engage with the cap plate to secure the at least one threaded connector to the cap plate.
In one embodiment, the connectors are polished by chemical polishing.
In one embodiment, the battery pack also includes at least one tap that supports the protection circuit module to the bare cell, wherein the at least one tap includes an opening that receives the threaded shaft of the at least one threaded connector.
In one embodiment, the threaded connector can comprise one or more screws.
In one embodiment, the battery pack also includes a cap that is positioned within the opening of the cover so that the cap is interposed between the exterior of the opening and the at least one threaded connector.
In another embodiment, the invention comprises a method of making a battery pack that includes providing at least one threaded connector that is dimensioned to be used to secure a cover and a protection circuit module to a bare cell of a battery pack. The method further comprises polishing the at least one threaded connector to polish the threads of the at least one threaded connector so as to control the size of the threads of the at least one threaded connector.
In one embodiment, the step of polishing the at least one threaded connector comprises chemically polishing the threaded connector.
These and other objects and advantages of the battery pack will become more apparent from the following description taken in conjunction with the accompanying drawings.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings.
According to an embodiment of the present invention, a battery pack 100 relates to tapping screws 141 and 142 for coupling a bare cell 110 and a case 150, and to a method of manufacturing the tapping screws 141 and 142. Hereinafter, the battery pack 100 will be described with reference to
The bare cell 110 includes an electrode assembly (not shown) and a sealing assembly 111 accommodating the electrode assembly. The electrode assembly may be formed by winding a positive electrode plate (not shown), a negative electrode plate (not shown), and a separator (not shown) in a known manner.
The sealing assembly 111 may include a cap plate 111a and a metal type can 111b and may be formed of a conductive material, for example, aluminum. The metal type can 111b has an open end, and the cap plate 111a covers the open end of the metal type can 111b. An electrode terminal 114 that is insulated by an insulator 114a may be formed in either the metal type can 111b or the cap plate 111a.
Referring to
In the current embodiment, the electrode terminal 114 is electrically connected to the negative electrode plate of the electrode assembly of the bare cell 110 to be a negative electrode P−, and the sealing assembly 111 is electrically connected to the positive electrode plate of the electrode assembly of the bare cell 110 to be a positive electrode P+, but the present invention is not limited thereto. In other words, the bare cell 110 may be a rectangular battery in which the electrode assembly is sealed by the sealing assembly 111 formed of a metal material, and in which any one of the positive electrode plate and the negative electrode plate of the electrode assembly is electrically connected to the sealing assembly 111, and the other plate is connected to the electrode terminal 114.
In this embodiment, the bare cell 110 may be a secondary battery. For example, the bare cell 110 may be an ion battery or a lithium polymer battery. However, the present invention is not limited thereto. Thus, the bare cell 110 may be a secondary battery such as a nickel (Ni)-cadmium (Cd) battery, a Ni-metal hydride (MH) battery, or the like.
In this embodiment, one surface of the cap plate 111a of the bare cell 110 may include at least one selected from the group consisting of screw receiving openings 112 and 113. Referring to
The protection circuit substrate 120 may include an insulating substrate 121, a printed circuit pattern (not shown), a conductive pad 123, a protection circuit unit 124, a charging/discharging terminal 125, and first and second taps 131 and 132. The conductive pad 123, the protection circuit unit 124, and the charging/discharging terminal 125 may be soldered to the printed circuit pattern formed on the insulating substrate 121. The protection circuit substrate 120 may be electrically connected to the bare cell 110. That is, a negative electrode of the protection circuit substrate 120 may be electrically connected to the electrode terminal 114, which is the negative electrode P− of the bare cell 110, by a lead tap 120a, and a positive electrode of the protection circuit substrate 120 may be electrically connected to the sealing assembly 110, which is the positive electrode P+ of the bare cell 110, by the first tap 131. A positive temperature coefficient (PTC) device 120a1 is electrically connected between the negative electrode of the protection circuit substrate 120 and the electrode terminal 114 and may block the electrical connection between the negative electrode of the protection circuit substrate 120 and the electrode terminal 114 when the temperature thereof is excessively high or a current excessively flows therethrough. The protection circuit unit 124 may selectively comprise a passive device such as a resistor, a capacitor, or the like, an active device such as a field-effect transistor, a safety device such as the PTC device 120a1, and integrated circuits. The protection circuit unit 124 charges or discharges the bare cell 110 when the bare cell 110 is to be charged/discharged, and blocks a charging/discharging path in the bare cell 110 when the bare cell 110 is overheated or is in an overcurrent state, thereby protecting the bare cell 110 from lifetime degradation, overheating, exploding, and the like.
The first and second taps 131 and 132 are respectively formed on different ends of the protection circuit substrate 120 to electrically connect the protection circuit substrate 120 and the bare cell 110. First and second coupling holes 131a and 132a may be formed in the first and second taps 131 and 132 corresponding to the screw receiving openings 112 and 113, respectively. Referring to
Both the first and second taps 131 and 132 may be formed of Ni or an alloy containing Ni, and may be soldered to the protection circuit substrate 120. In this case, in
The first and second tapping screws 141 and 142 include body parts 141a and 142a and head parts 141b and 142b. The body parts 141a and 142a of the first and second tapping screws 141 and 142 include a screw thread that is screw-coupled to the screw receiving openings 112 and 113 of the bare cell 110. The head parts 141b and 142b of the first and second tapping screws 141 and 142 are formed in an upper part of the body parts 141a and 142a, and have a diameter greater than those of the body parts 141a and 142a. In
A screw groove may be formed in an inner circumferential surface of the screw receiving opening 112 to be coupled with the first tapping screw 141. Alternatively, the screw groove is not formed, and the inner circumferential surface is formed to be smaller than an outside diameter of the first tapping screw 141, so that the screw thread of the first tapping screw 141 is coupled to the inner circumferential surface of the screw receiving opening 112 by cutting an outer surface of the screw groove. For example, the inner diameter of the screw receiving opening 112 of the cap plate 111a may be greater than an inner diameter of the body part 141a and less than an outside diameter of the body part 141a. Therefore, when the screw receiving opening 112 is coupled to the first tapping screw 141, the inner circumferential surface of the screw receiving opening 112 is deformed to be tightly adhered to the body part 141a of the first tapping screw 141. The cap plate 111a may include a light alloy, such as aluminum, so as to be easily deformed by the screw thread 141a1 of the first tapping screw 141.
The cover case 150 includes at least one selected from the group consisting of first and second holes 151a and 152a. Mounting grooves 151b and 152b are formed outside of the first and second holes 151a and 152a. For example, the mounting grooves 151b and 152b are formed to have inner diameters greater than those of the first and second holes 151a and 152a so as to support head parts 141b and 142b of the first and second tapping screws 141 and 142. Hereinafter, the mounting grooves 151b and 152b will be referred to as a first mounting groove 151b and a second mounting groove 152b, respectively. The first tapping screw 141 may be coupled to the first screw receiving groove 112 formed in the bare cell 110 after passing through the first hole 151a formed in the cover case 150 and the first coupling hole 131a formed in the first tap 131. The head part 141b of the first tapping screw 141 may be tightly adhered to the first mounting groove 151b of the cover case 150. The second tapping screw 142 may be coupled in a similar manner. Therefore, the first tapping screw 141 and the second tapping screw 142 couple the cover case 150 to the bare cell 110. The cover case 150 is, in one embodiment, a plastic case made by molding a resin material such as polycarbonate, and protects the protection circuit substrate 120 from an external impact and protects against a short circuit in the protection circuit substrate 120.
Referring to
In this case, the contact resistance between the first and second taps 131 and 132 and the bare cell 110 may be measured through a random free fall (RFF) test. The RFF test is performed by dropping six battery packs 100 at the same time from a height of 1 meter two hundred times to measure contact resistance. In this case, the structure of the battery pack 100 may be controlled so that variation of the contact resistance obtained by the RFF test is less than a predetermined value. The variation of the contact resistance may be controlled to be less than 14 ma Table 1 shows results of the RFF test performed on the battery pack 100.
As shown in Table 1, contact resistances of four battery packs 100, from among the six battery packs 100, were poor. In this case, the sizes of the battery packs 100 used in the RFF test will be described with reference to Table 2 and
Here, the sizes of the bare cell 110 and the case 150 may have values within a predetermined range, so that the bare cell 110 and the case 150 may be uniformly mounted on a jig of an engaging device. In this case, the weight of the battery pack 100 is about 26 g.
A coupled state between the first tap 131 and the cap plate 111a before and after performing the RFF test will be described with reference to
Table 3 shows values of outer diameters (OD) and inner diameters (ID) of an embodiment 4-1 and comparative examples 4-2 and 4-3. Referring to
Referring to Table 3, in the embodiment 4-1, a chemical polishing process is performed, and a plating thickness is 5.5 um. In the comparative example 4-2, a chemical polishing process is not performed, and a plating thickness is 2.5 um. In the comparative example 4-3, a chemical polishing process is not performed, and a plating thickness is 4.5 um. When the embodiment 4-1 is applied to the battery pack 100, an error rate of the battery pack 100 is 2,000 ppm (parts-per-million). On the other hand, when the comparative examples 4-2 and 4-3 are applied to the battery pack 100, the error rate of the battery pack 100 is 20,000 ppm. As such, the difference of the error rate shows that surface states of the first and second tapping screws 141 and 142 are changed according to whether or not the chemical polishing process has been performed, and thus the surface states of the first and second tapping screws 141 and 142 affect the error rate of the battery pack 100. In general, when small-sized first and second tapping screws 141 and 142 are manufactured, a chemical polishing process is not performed. However, a chemical polishing process may be added when the small-sized first and second tapping screws 141 and 142 are manufactured, so as to control surface roughnesses of the first and second tapping screws 141 and 142. In this case, the small-sized first and second tapping screws 141 and 142 may be tapping screws each having a height of less than 6 mm.
A method of manufacturing the small-sized first and second tapping screws 141 and 142 will now be described with reference to
First, a raw material for forming the first and second tapping screws 141 and 142 is prepared. The raw material may be carbon steel such as SWCH18A. The head part 141b may be formed by processing the raw material (S501). A screw thread may be formed by performing a rolling process (S503). A thermal treatment may be performed on the first and second tapping screws 141 and 142 through quenching (HV800) and tempering (HV 500˜520) processes (S505). Then, sizes of the first and second tapping screws 141 and 142 may be processed through a chemical polishing process (S507). Then, a plating process may be performed thereon in order to prevent metal oxidization (S509).
Table 4 shows values of outer diameters OD and inner diameters ID of the tapping screw through the rolling (S503), chemical polishing process (S507) and plating process (S509).
Referring to Table 4, a variation of the outer diameters OD of the first and second tapping screws 141 and 142 is greatest during the chemical polishing process. This is because an area of a peak of the screw thread 141a1 is small compared to the inner diameters ID of the first and second tapping screws 141 and 142, and thus the variation of the outer diameter OD decreasing due to the chemical polishing process (S507) is great. The variation of the inner diameters ID of the first and second tapping screws 141 and 142 is greatest during the plating process. Since a surface of the body part 141a is advantageous to deposition of plating during the plating process (S509), the variation of the inner diameter ID may be great during the plating process (S509). Referring to
The chemical polishing process (S507) will now be described in detail with reference to
The chemical polishing process of
According to the chemical polishing process (S507) of this embodiment of the present invention, the major factors affecting the chemical polishing process (S507) may be controlled so as to process the sizes of the first and second tapping screws 141 and 142 and to control the surface roughnesses thereof. That is, as shown in Table 4, the outer diameters and the inner diameters of the first and second tapping screws 141 and 142 are changed through the chemical polishing process (S507), and the sizes of the first and second tapping screws 141 and 142 may be processed in consideration of factors affecting the variation of the outer diameters and the inner diameters of the first and second tapping screws 141 and 142. In this case, the factors affecting the chemical polishing process (S507) may be concentration and temperature of the polishing solution used in the chemical polishing process and time for the reaction between the polishing solution and the tapping screws 141 and 142 (S507).
Table 5 shows a variation of the outer and inner diameters and the surface roughnesses of the first and second tapping screws 141 and 142 according to the concentration of the polishing solution in the chemical polishing process (S507).
When the concentration of the polishing solution is 5 through 9, the sizes and surface roughnesses of the first and second tapping screws 141 and 142 are good. The concentration may be measured through a Baum's hydrometer. A weight of a material at a predetermined temperature is a unique value of the material. Accordingly, purity of the polishing solution may be checked by measuring the weight. That is, the weight may be measured by using a relation between the weight and concentration of the polishing solution.
Referring table 6, the concentration of the polishing solution may vary according to a composition ratio of ammonium hydrogen-fluoride, hydrogen peroxide and water.
Table 7 shows a variation and surface roughnesses of the outer and inner diameters of the first and second tapping screws 141 and 142 according to a temperature of the polishing solution.
When a temperature of the polishing solution is 30° C. through 50° C., the first and second tapping screws 141 and 142 had preferable sizes and surface roughnesses. That is, the sizes and surface roughnesses of the first and second tapping screws 141 and 142 may be controlled by controlling the temperature of the polishing solution during the chemical polishing process (S507).
Table 8 shows a variation of outer and inner diameters and surface roughnesses of the first and second tapping screws 141 and 142 according to time.
Referring to Table 8, when time is 10 s through 15 s, the first and second tapping screws 141 and 142 had preferable sizes and surface roughnesses.
Accordingly, referring to Tables 5 through 8, when the concentration is through 9, when the temperature of the polishing solution is 30° C. through 50° C., and when the time for the reaction between the polishing solution and the tapping screws 141 and 142 is 10 s through 15 s, the first and second tapping screws 141 and 142 had preferable sizes and surface roughnesses. Also, values of the sizes and surface roughnesses of the first and second tapping screws 141 and 142 may be obtained by satisfying the concentration and temperature of the polishing solution and time for the reaction between the polishing solution and the tapping screws 141 and 142.
Now, a condition in which the concentration is 5 through 9, the temperature is 30° C. through 50° C., and the time for the reaction between the polishing solution and the tapping screws 141 and 142 is 10 s through 15 s, is defined as a first condition. For example, the outer diameters OD of the first and second tapping screws 141 and 142 having undergone the chemical polishing process (S507) according to the first condition may be 1.22 mm through 1.27 mm, and the inner diameter ID thereof may be 0.88 mm through 0.93 mm. In more detail, the outer diameter OD may be 1.226 mm through 1.235 mm, and the inner diameter ID may be 0.889 mm through 0.895 mm. However, the present invention is not limited thereto. Thus, since the concentration and temperature of the polishing solution and time for the reaction between the polishing solution and the tapping screws 141 and 142 may affect the sizes and surface roughnesses of the first and second tapping screws 141 and 142, the first and second tapping screws 141 and 142 may be manufactured by controlling the concentration and temperature of the polishing solution and time for the reaction between the polishing solution and the tapping screws 141 and 142.
Coupling and a coupling error rate of the first and second tapping screws 141 and 142 coupled with a light alloy metal are significantly different according to surface precision of the first and second tapping screws 141 and 142. That is, minute burs, external substances, etc. generated during the manufacturing process of the first and second tapping screws 141 and 142 undergo the chemical polishing process (S507), and thus the shape of the screw threads 141a1 of the first and second tapping screws 141 and 142 are rounded and the surfaces of the screw threads 141a1 are smoothened. Accordingly, frictional resistance generated when the first and second tapping screws 141 and 142 are coupled with the light alloy metal and damage to the light alloy metal are minimized, thereby improving coupling of the first and second tapping screws 141 and 142. For example, the first and second tapping screws 141 and 142 having undergone the chemical polishing process (S507) according to the first condition may have clamping force of about 180 N when being coupled with the first and second screw receiving openings 112 and 113.
Table 9 shows a result of the RFF test performed on the battery pack 100 using the first and second tapping screws 141 and 142 whose sizes are processed through the chemical polishing process (S507), under the first condition.
Compared to the result of Table 1, the results of Table 9 are significantly improved.
Also, the battery pack 100 has a coupling error rate of less than about 1,000 ppm during a coupling process, and thus process stability has been improved.
It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.
This application claims the benefit of U.S. Provisional Patent Application No. 61/310,193, filed Mar. 3, 2010 entitled BATTERY PACK AND METHOD OF MANUFACTURING SAME which is hereby incorporated in its entirety by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61310193 | Mar 2010 | US |
