Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, and the manufacturing costs of the pouch-shaped battery are low.
FIG. 1 is a perspective view typically illustrating a conventional pouch-shaped battery. A pouch-shaped battery 10 shown in FIG. 1 is configured in a structure in which two electrode leads 11 and 12 protrude from the upper and lower ends of a battery body 13, respectively, while the electrode leads 11 and 12 are opposite to each other. A sheathing member 14 includes upper and lower sheathing parts. That is, the sheathing member 14 is a two-unit member. An electrode assembly (not shown) is received in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 14. The opposite sides 14b and the upper and lower ends 14a and 14c, which are contact regions of the upper and lower sheathing parts of the sheathing member 14, are bonded to each other, whereby the pouch-shaped battery 10 is manufactured. The sheathing member 14 is configured in a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 may be bonded to each other using a bonding agent. For the opposite sides 14b of the sheathing member 14, the same resin layers of the upper and lower sheathing parts of the sheathing member 14 are in direct contact with each other, whereby uniform sealing at the opposite sides 14b of the sheathing member 14 is accomplished by welding. For the upper and lower ends 14a and 14c of the sheathing member 14, on the other hand, the electrode leads 11 and 12 protrude from the upper and lower ends 14a and 14c of the sheathing member 14, respectively. For this reason, the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 are thermally welded to each other, while a film-shaped sealing member 16 is interposed between the electrode leads 11 and 12 and the sheathing member 14, in consideration of the thickness of the electrode leads 11 and 12 and the difference in material between the electrode leads 11 and 12 and the sheathing member 14, so as to increase sealability of the sheathing member 14.
A battery module is a structural body including a plurality of battery cells which are combined with each other, with the result that the safety and operating efficiency of the battery module may be lowered when overvoltage, overcurrent, and overheating occur in some of the battery cells. Consequently, a sensing unit for sensing the overvoltage, overcurrent, and overheating is needed. For example, a voltage sensor or a temperature sensor is connected to the battery cells so as to sense and control the operation of the battery cells in real time or at predetermined time intervals. However, mounting or connection of such a sensing unit complicates assembly of the battery module. Furthermore, a possibility of occurrence of a short circuit is increased due to a plurality of wires necessary to mount or connect the sensing unit.
Specifically, some conventional arts have proposed battery modules in which a voltage sensor contacts electrode leads of a battery cell in a point contact manner via a spring to sense voltage of the battery cell, a voltage sensor contacts electrode leads of a battery cell via a bolt and a rivet, or a voltage sensor is connected to electrode leads of a battery cell by welding. For example, Japanese Patent Application Publication No. 2005-116440 discloses an assembled battery configured in a structure in which a plurality of single batteries are stacked, wherein a plurality of voltage sensing terminals for sensing voltages of the single batteries are arranged in the stacking direction of the single batteries, and the voltage sensing terminals are provided with a voltage sensing line withdrawal unit for connecting the voltage sensing terminals to an external device in a bundle.
In the above publication, however, the voltage sensing terminals are electrically connected to electrode tabs of the respective single batteries by ultrasonic welding. As a result, the electrode tabs of the respective single batteries may be deformed. Also, a space in which the above members are to be coupled, welded, or soldered for electrical connection is needed, with the result that the overall size of the system is increased, which is not preferable. Consequently, there is a high necessity for a battery module which has a more compact size and exhibits high structural stability.
In addition, for devices, such as vehicles, to which external force, such as vibration or impact, is continuously applied, the increase in contact resistance at the electrical connection region may cause unstable output and occurrence of a short circuit. Also, sensing defects may occur due to accumulation of moisture generated during use of the battery module for a long period of time.