SECONDARY BATTERY HAVING IMPROVED ELECTRIC

CONDUCTIVITY AND ELECTRICAL CONDUCTOR PLATE

ELECTRICALLY CONNECTING ELECTRONIC PARTS

Technical Field

[1] The present invention relates to a secondary battery and an electrical connector plate, and more particularly to a structure capable of improving electric conductivity, adhesion and corrosion resistance of a connection member (or, an electrical connector plate) that electrically connects components of a secondary battery. Background Art

[2] Generally, mobile electronic products such as video camera, mobile phone and portable PC have light weight structure and intelligent functions. In addition, along with the development of electric automobiles, many researches are progressed for batteries used as a power source of such electronic products or electric automobiles. In particular, interests are focused on a secondary battery that allows repeated charging and discharging, and researches for electrodes and batteries with improved capacity density and specific energy are also under progress.

[3] Among secondary batteries, a lithium ion battery developed in the early 1990' s is now standing in the spotlight due to its advantages such as high operation voltage and far better energy density rather than conventional batteries such as Ni-MH battery, Ni- Cd battery and sulfuric acid- lead battery that use electrolytic solution.

[4] Such a secondary battery generally includes an electrode cell having a positive electrode and a negative electrode therein, protective elements such as a PTC (Positive Temperature Coefficient) element and PCM (Protection Circuit Module) acting as components in the battery for protecting the battery against overcurrent or overvoltage flowing in or out, an external connector having external I/O terminals and metal leads for electrically connecting them.

[5] The metal leads are used for electrically connecting components of the secondary battery such as an electrode cell, protective elements and external connectors. Particularly, the metal leads require electrical and chemical corrosion resistance against materials such as electrolyte or moisture, and nickel is generally used.

[6] However, a material with good corrosion resistance such as nickel is used for the metal lead, the metal lead has bad electric conductivity, which results in increase of an internal resistance of the entire battery. Meanwhile, in case a material with good electric conductivity is used for the metal lead, there arise problems that the metal lead has bad adhesion to other components and deteriorated corrosion resistance.

Disclosure of Invention

Technical Problem

[7] The present invention is designed in consideration of the above problems, and therefore it is an object of the invention to provide a secondary battery including a connection member with an improved electric conductivity as well as excellent adhesion and corrosion resistance.

[8] In addition, another object of the present invention is to provide an electrical conductor plate for electrically connecting components of an electronic product such as a secondary battery, which has improved adhesion and corrosion resistance as well as improved electric conductivity. Technical Solution

[9] In order to accomplish the above object, the present invention provides a secondary battery, which includes a cell including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and provided with positive and negative electrode terminals exposed out; an external connector connected to the positive and negative electrode terminals to give a charging/discharging terminal; and a connection member for electrically connecting the terminal of the cell with the external connector, wherein the connection member includes a first metal layer, and a second metal layer laminated on one surface of the first metal layer and having a specific resistance higher than the first metal layer and an oxidation-reduction level lower than the first metal layer.

[10] Preferably, the first metal layer is made of copper or its alloy, and the second metal layer is made of nickel.

[11] In another aspect of the present invention, there is also provided an electrical connector plate for electrically connecting electronic parts, which includes a first metal layer having a plate shape; and a second metal layer formed on one surface of the first metal layer, wherein the first metal layer has a specific resistance lower than the second metal layer, and the second metal layer has an oxidation-reduction level lower than the first metal layer. Brief Description of the Drawings

[12] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

[13] FIGs. 1 and 2 are sectional views schematically showing a secondary battery according to a preferred embodiment of the present invention; and

[14] FIGs. 3 to 5 are sectional views schematically showing a connection member having a plating layer formed thereon according to preferred embodiments of the

present invention.

Best Mode for Carrying Out the Invention

[15] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[16] FIG. 1 schematically shows a secondary battery according to one embodiment of the present invention.

[17] Referring to FIG. 1, the secondary battery according to this embodiment includes a secondary battery cell 100, a protective element 200, an external connector 400 and a connection member 300 for electrically connecting them.

[18] The secondary battery cell 100 is configured with a positive electrode, a negative electrode and a separator for separating them, which are respectively laminated in at least one layer, and two electrode terminals 110, 120 are provided thereto. These two electrode terminals are respectively connected to a positive electrode and a negative electrode mounted in each cell. In addition, one of the electrode terminals 110 is connected to the connection member 300, while the other 120 is connected to a PTC element 220 that is a protective element.

[19] Here, the secondary battery cell 100 is a container pack that seals a cell composed of a positive electrode, a negative electrode and a separator, or their laminate together with electrolyte. The protective element 200 and the connection member 300 are attached to an outside of the container pack to be included in an outer case, but the present invention is not limited thereto. For example, it is also possible that the secondary battery cell 100 shown in FIG. 1 is a laminate of a positive electrode, a negative electrode and a separator, and the secondary battery cell 100 and the protective element 200 are received in the container pack together with electrolyte.

[20] In this embodiment, the protective element 200 employs a PTC element 220 and a

PCM 210. The PTC element 220 includes a PTC material layer 221 composed of a mixture of polymer resin and conductive material to increase an electric resistance as temperature rises, and first and second PTC leads 222A, 222B connected to electrodes respectively formed on both surfaces of the PTC material layer.

[21] Here, the PTC material layer 221 is composed of polymer resin in which conductive particles are dispersed to give a PTC nature electrically. The polymer resin may use polyethylene, polypropylene, ethylene/propylene polymer and so on, and the conductive particles may use particles of carbon black or other metal materials.

[22] The first and second leads 222A, 222B positioned above and below the PTC element 220 are made of metal such as aluminum, nickel, copper or their alloys or metal compound, and they are used for electrically connecting the positive or negative terminal 120 of the secondary battery cell 100 and the PCM 210, or the external connector 400 and the PTC element 220.

[23] Meanwhile, the above PTC element 220 is illustrated to have a thin rectangular parallelepiped shape such that the first and second leads 222A, 222B are oppositely protruded in a longitudinal direction, but the shape of the PTC element 220 and the protrusion direction of the leads may be changed in various ways depending on shape and attachment position of the PTC element 220.

[24] In addition, the PCM 210 is a circuit element for preventing explosion or firing of the battery caused by overcurrent or overvoltage, and it is not explained in detail here since its configuration is well known in the art and it is not an essential part of the present invention.

[25] The external connector 400 has charging/discharging terminals, and it is provided as a part of an outer case or separately from the outer case.

[26] The connection member 300 is connected to one electrode terminal 110 of the secondary battery cell 100 and one terminal of the PCM 210, and then electrically connected to the external connector 400.

[27] Meanwhile, in this embodiment, the PTC element 220 and the PCM 210 are all used as the protective element, but they may be selectively used, and their connection and arrangement may be changed in various ways. For example, in case only the PTC element 220 is used as the protective element, it is possible that the PCM 210 is excluded in FIG. 1 and the connection member 300 is directly connected to the external connector 400, or it is also possible that the connection member 300 is interposed between the PTC element 220 and the electrode terminals 110 or 120 of the secondary battery cell 100.

[28] Here, the connection member 300 is arranged close to the secondary battery cell

100 as shown in FIG. 1, so a second metal layer 320 is formed only one side of the connection member 300, which is relatively exposed to chemical materials, thereby preventing corrosion of the connection member 300. At this time, when the connection member 300 is arranged close to the secondary battery cell 100, the connection member 300 is closely adhered to the secondary battery cell 100 so that the other surface of the connection member 300 is not exposed as possible within the range that

the secondary battery cell 100 and the connection member 300 keep electric insulation by interposing an insulation material such as an insulation tape (not shown) between them, for example.

[29] FIG. 2 schematically shows a secondary battery according to another embodiment of the present invention. Here, the same reference numeral as in FIG. 1 designates the same component with the same structure and function.

[30] Referring to FIG. 2, the connection member 300 includes a first metal layer 310 having good electric conductivity, and a second metal layer 320 and a third metal layer 330 laminated on both sides of the first metal layer and having good adhesion and strong oxidation force in electrical and chemical aspects. This configuration can surely protect both sides of the connection member 300 against corrosion, so the connection member 300 may not be closely adhered to the secondary battery cell 100, as shown in FIG. 2.

[31] As mentioned above, the connection member 300 should have good electric conductivity so as to lower the entire resistance of the secondary battery, and also it should have good adherence to a metal surface of a part prepared therein. In addition, the connection member 300 should have good corrosion resistance against chemical material such as electrolyte.

[32] Now, the connection member 300 requiring such characteristics will be described in more detail with reference to FIGs. 3 to 5.

[33] Referring to FIG. 3, the connection member 300 includes a first metal layer 310 made of metal with good electric conductivity, and a second metal layer 320 made of material with good adhesion and strong oxidation force in electric and chemical aspects.

[34] The first metal layer 310 is preferably made of copper, gold, silver, or their alloy, which has a specific resistance of 3 μΩD or below at a room temperature, so as to have good electric conductivity.

[35] The second metal layer 320 is a metal layer laminated on one surface of the first metal layer 310 and it is used for improving insufficient features of metal with good electric conductivity, namely for improving adhesion and corrosion resistance. This second metal layer 320 may be laminated using electroplating, electroless plating, sputtering or lamination.

[36] As shown in FIG. 1, the second metal layer 320 formed on a surface that is adhered to a metal surface of the electrode terminal 110 or 120 or other parts, so a metal with good adhesion is used for the second metal layer 320. Specifically, in order to adhere the connection member 300 with other parts, spot welding is generally used, which may prevent inferior adhesion when a resistance of the adhesion surface is great during the adhesion process. Thus, the second metal layer 320 is preferably made of metal or

compound having a specific resistance of 2 to 30 μΩD, which is greater than the specific resistance of the first metal layer 310. If the specific resistance of the metal is not greater than 2 μΩD, adhesion using resistance is bad, while, if the specific resistance is not less than 30 μΩD, the entire resistance of the connection member 300 is increased.

[37] In addition, the second metal layer 320 should have good corrosion resistance since it is formed on an exposed surface of the connection member 300 as shown in FIG. 1. Specifically, when OV is set as a criterion hydrogen oxidation-reduction level, the second metal layer 320 is made of metal or compound whose oxidation-reduction level is -2.0 to OV, which is lower than that of copper (0.52V), gold (1.5V), silver (0.8V) or the like, composing the first metal layer 310. That is to say, the second metal layer 320 uses metal whose oxidation-reduction level is lower than that of the first metal layer 310 so as to protect the first metal layer 310 against corrosion caused by external oxidation-reduction reaction.

[38] In addition, the second metal layer 320 preferably has a thickness of 0.1 to 100 D so as to keep the corrosion resistance characteristic together with not increasing a resistance of the connection member. For example, in case the second metal layer is formed using an electroplating manner, its thickness is preferably 1 to 10 D. However, the thickness of the second metal layer is not limited to the above range. For example, it is important that the second metal layer 320 is set not to disturb excellent resistance characteristics caused by the first metal layer 310 with good electric conductivity, together with supplementing adhesion or corrosion resistance, which is deficient in the first metal layer 310. Thus, the thickness of the second metal layer 320 is preferably about 1/10 to 1/1000 of that of the first metal layer 310, though it depends on an electronic product to which the connection member of the present invention is applied.

[39] Referring to FIG. 4, the connection member 300 includes a first metal layer 310 using a metal with good electric conductivity, a second metal layer 320 laminated on one surface of the first metal layer 310 and having good adhesion and strong oxidation force in electric and chemical aspects, and a third metal layer 330 laminated on the other surface of the first metal layer 310 and having strong oxidation force in electric and chemical aspects.

[40] The second metal layer 320 is laminated on one surface of the first metal layer 310 so that its surface is adhered to other parts. The third metal layer 330 is laminated on the other surface of the first metal layer 310 so as to prevent corrosion when the connection member 300 is exposed to chemical materials.

[41] The third metal layer 330 may also be formed on the other surface of the first metal layer 310 by means of electroplating, electroless plating, sputtering or lamination, like the second metal layer 320.

[42] In case one surface of the connection member 300 is closely arranged, for example adhered, to a container pack of the secondary battery cell 100, the second metal layer 320 may be laminated on only one surface of the connection member 300 relatively exposed to chemical materials, as shown in FIG. 2. However, it is more preferred that, as shown in FIG. 4, the second metal layer 320 with good adhesion and corrosion resistance is laminated on one surface of the first metal layer 310 adhered to other parts, and the third metal layer 330 with good corrosion resistance is laminated on the other surface, since this configuration may more surely prevent corrosion of the connection member. Furthermore, it is more preferred that the third metal layer 330 has good adhesion together with good corrosion resistance.

[43] Referring to FIG. 5, the connection member 300 includes a first metal layer 310 made of metal with good electric conductivity, and second and third metal layers 320, 330 respectively laminated on both surfaces of the first metal layer 310 and made of the same material with good adhesion and strong oxidation force in electric and chemical aspects. That is to say, though it is illustrated in the embodiment of FIG. 4 that the second metal layer 320 and the third metal layer 330 are made of different metal layers with good adhesion and corrosion resistance, the metal layers formed on both surfaces of the first metal layer 310 may be made of the same metal layer with good adhesion and corrosion resistance. In this case, there is no need to distinguish an adhesion surface when the connection member 300 is adhered to parts of the secondary battery, thereby making it easier to assemble the battery.

[44] As mentioned above, the connection member 300 of the present invention is configured such that the first metal layer 310 with good electric conductivity, the second metal layer 320 with good adhesion and corrosion resistance and the third metal layer 330 selectively having good corrosion resistance are laminated, thereby improving its electric conductivity together with keeping excellent corrosion resistance and good adhesion. Mode for the Invention

[45] To compare performance of the secondary battery according to the present invention with that of a conventional secondary battery, the following experiments were conducted.

[46] As for a connection member for electrically connecting a secondary battery cell to a protective element, copper with a low specific resistance of 1.7 μΩD was prepared in a thin film shape with a thickness of 0.125 mm as a first metal layer. Then, second metal layer was laminated on both surfaces of the prepared first metal layer according to the following embodiments.

[47]

[48] Embodiment 1

[49] A first metal layer was formed using a thin copper foil with a specific resistance of

1.7 μΩD and a thickness of 0.125 mm, and then second and third metal layers were formed by plating nickel with a specific resistance of 6.9 μΩD and an oxidation- reduction level of -0.23V on both surfaces of the first metal layer into a thickness of 1 D.

[50]

[51] Embodiment 2

[52] A first metal layer was formed using a thin copper foil with a specific resistance of

1.7 μΩD and a thickness of 0.125 mm, and then second and third metal layers were formed by plating lead with a specific resistance of 20.6 μΩD and an oxidation- reduction level of -0.13V on both surfaces of the first metal layer into a thickness of 1 D.

[53]

[54] Embodiment 3

[55] A first metal layer was formed using a thin copper foil with a specific resistance of

1.7 μΩD and a thickness of 0.125 mm, and then second and third metal layers were formed by plating aluminum with a specific resistance of 2.7 μΩD and an oxidation- reduction level of -1.66V on both surfaces of the first metal layer into a thickness of 1 D.

[56]

[57] Comparative Example 1

[58] Nickel used as a usual metal lead in the prior art was prepared in a thin film shape with a thickness of 0.125 mm.

[59]

[60] Comparative Example 1

[61] A first metal layer was formed using a thin copper foil with a specific resistance of

1.7 μΩD and a thickness of 0.125 mm, and both surfaces of the first metal layer were not plated.

[62]

[63] Five samples prepared as mentioned above were made into test pieces with a width of 3 mm and a length of 60 mm, and then their resistance characteristics in a longitudinal direction were measured. Then, each test piece was adhered to the prepared nickel lead by means of spot welding, and then its adhesion strength was measured. Also, in order to evaluate a corrosion resistance, each test piece was dipped in a prepared electrolyte and then conducted the cyclic voltametric test with increasing a voltage from 2.5V to 4.5V at a rate of 500 D/sec, and then the degree of corrosion of each test piece was observed.

[64] Table 1 shows evaluation results of the test pieces for voltage, adhesion to metal, and corrosion resistance. In Table 1, the adhesion shows relatively values of the test pieces, and the corrosion resistance is evaluated as 'good' when corrosion is observed by the naked eyes and as 'bad' when corrosion is not observed.

[65] [66] Table 1

[67] [68] As shown in Table 1, in case of the embodiments 1 to 3, when the second metal layer using nickel, lead and aluminum, which respectively have specific resistances of 6.9 μΩD, 20.6 μΩD and 2.7 μΩD greater than 1.7 μΩD that is a specific resistance of copper, and which respectively have oxidation-reduction levels of -0.23V, -0.13V and -1.66V, lower than 0.52V that is an oxidation-reduction level of copper, are formed on both surfaces of the first metal layer made of copper with a thickness of 0.125 mm, they showed satisfactory results in electric conductivity, adhesion and corrosion resistance.

[69] On the contrary, in case of the comparative example 1, when no metal was plated on the first metal layer made of nickel with a thickness of 0.125 mm, its entire resistance was too great though there is no problem in adhesion and corrosion resistance. In addition, in case of the comparative example 2, when no metal was plated on the first metal layer made of copper with a thickness of 0.125 mm, adhesion and corrosion resistance were not good though electric conductivity showed no

problem.

[70] Thus, considering the whole results of the embodiments and the comparative examples, it would be understood that better results may be obtained when a metal with a lower resistance is arranged inside and a metal with a higher resistance and a lower oxidation-reduction level is arranged outside. In particular, it would be understood that a connection member most excellent in electric conductivity, adhesion and corrosion resistance can be obtained when copper or its alloy is used for the first metal layer and nickel is used for the second or third metal layer. Industrial Applicability

[71] According to the present invention, a connection member for connecting components of an electronic part such as a secondary battery is configured with a metal layer with good electric conductivity and a metal layer with good corrosion resistance and/or good adhesion laminated on one or both surfaces of the above metal layer, thus reducing the entire resistance of the electronic part such as a secondary battery together with improving corrosion resistance and adhesion.