Patent Publication Number: US-2010112420-A1

Title: Internal pressure measuring apparatus for secondary battery

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments relate to an internal pressure measuring apparatus for a secondary battery, and more particularly, to an internal pressure measuring apparatus for a secondary battery capable of measuring internal pressure variation of a secondary battery in real time based on external environments after injection of an electrolyte. 
     2. Description of the Related Art 
     In recent times, compact and lightweight mobile electric/electronic appliances, e.g., cellular phones, notebook computers, camcorders, etc., have been widely developed and manufactured. In order to operate the mobile electric/electronic appliances even when there is no separate power supply available, a battery pack is built-in. The battery pack may include, e.g., a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni-MH) battery, or a lithium (Li) battery. In consideration of economic feasibility, the battery pack may generally be a secondary battery, which can be repeatedly charged and discharged. 
     The lithium (Li) secondary battery is widely used for the mobile electric/electronic appliances because of the advantages the lithium secondary battery has over the Ni—Cd battery and the Ni-MH battery. The lithium secondary battery has an operation voltage about three times larger than that of the Ni—Cd battery or the Ni-MH battery. Also, the lithium secondary battery has energy density per unit weight, which is larger than that of the Ni—Cd battery or the Ni-MH battery. The lithium secondary battery may be classified based on the kind of electrolyte, e.g., a lithium ion battery using a liquid electrolyte or a lithium polymer battery using a polymer electrolyte. The lithium secondary battery may be further classified based on the shape thereof, e.g., a cylinder type battery, a prismatic type battery, or a pouch type battery. 
     The secondary battery generally includes an electrode assembly, a can containing an electrolyte in which lithium ions can move between electrodes of the electrode assembly, and a cap assembly for sealing the can. The electrode assembly includes a positive electrode plate having a positive electrode collector with positive electrode active materials applied thereto and a positive electrode tab electrically connected to one side of the positive electrode collector. The electrode assembly further includes a negative electrode plate having a negative electrode collector with negative electrode active materials applied thereto and a negative electrode tab electrically connected to one side of the negative electrode collector. A separator may be disposed between the two electrode plates in the electrode assembly. 
     Since the secondary battery is completed by coupling the cap assembly to the can where the electrode assembly is housed, injecting an electrolyte through an electrolyte inlet port of the cap assembly, and then, sealing the electrolyte inlet port, it is difficult to measure internal pressure variation of the secondary battery based on external environments when the electrolyte is injected. 
     SUMMARY OF THE INVENTION 
     Embodiments are therefore directed to an internal pressure measuring apparatus for a secondary battery capable of measuring internal pressure variation of the secondary battery based on external environments when an electrolyte is injected. 
     It is therefore a feature of an embodiment to provide an internal pressure measuring apparatus for a secondary battery capable of precisely measuring the internal pressure of the secondary battery. 
     It is therefore another feature of an embodiment to provide an internal pressure measuring apparatus for a secondary battery capable of measuring internal pressure variation of the secondary battery in real time based on external environments when an electrolyte is injected. 
     At least one of the above features and other advantages may be realized by providing an internal pressure measuring apparatus for a secondary battery including a connection jig configured to be fastened to an electrolyte inlet port of the secondary battery, a pressure gauge displaying a measured internal pressure and a pipe connecting the connection jig to the pressure gauge and filled with a pressure medium. 
     The connection jig may include a projection configured to be inserted into the electrolyte inlet port. The connection jig may further include a sealing member surrounding the projection. The sealing member may be an insulator. 
     The projection may have a length shorter than a distance between the electrolyte inlet port of the secondary battery and an insulating case inside of the secondary battery. The length of the projection may be longer than a thickness of the cap plate of the secondary battery. The projection may have a spiral cone shape. 
     A fastening member may be disposed between the pressure gauge and the pipe and may adjust a fastening force between the pressure gauge and the pipe. 
     A storage medium may be electrically connected to the pressure gauge and may record the measured internal pressure. A display device may be electrically connected to the pressure gauge and may display an internal pressure variation of the secondary battery. The pressure medium may be fluid. The fluid may be oil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  illustrates a schematic cross-sectional view of an internal pressure measuring apparatus for a secondary battery in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 10-2008-0108414, filed on Nov. 3, 2008, in the Korean Intellectual Property Office, and entitled: “Internal Pressure Measuring Apparatus for Secondary Battery,” is incorporated by reference herein in its entirety. 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the length and thickness of layers and regions are exaggerated for clarity, and like reference numerals designate like elements throughout the specification. In addition, when a portion is described to be “connected” to the other portion, it means that the portion may be “directly connected” to the other portion, or may be “electrically connected” to the other portion with another device interposed therebetween. 
     Embodiments 
       FIG. 1  illustrates a schematic cross-sectional view of an internal pressure measuring apparatus for a secondary battery in accordance with an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the internal pressure measuring apparatus for a secondary battery in accordance with an exemplary embodiment of the present invention may include a connection jig  410  fastened to an electrolyte inlet port  354  of the secondary battery, a pressure gauge  420  measuring an internal pressure of the secondary battery, and a pipe  430  filled with a pressure medium, connecting the connection jig  410  to the pressure gauge  420 . 
     The secondary battery may include an electrode assembly  100 , a can  200  containing an electrolyte (not shown) in which lithium ions can move between electrodes of the electrode assembly  100  and having an upper opening, and a cap assembly  300  sealing the can  200  and having an electrode terminal  310  electrically connected to the electrode assembly  100 . The electrode assembly  100  may include a positive electrode plate  120  having a positive electrode tab  111  connected to a positive electrode collector (not shown) with positive electrode active materials (not shown) applied thereto, a negative electrode plate  110  having a negative electrode tab  112  connected to a negative electrode collector (not shown) with negative electrode active materials (not shown) applied thereto, and a separator  130  disposed between the positive electrode plate  120  and the negative electrode plate  110 . 
     The cap assembly  300  coupled to the upper opening of the can  200  may include a cap plate  350 , an insulating plate  340 , a terminal plate  330 , an insulating case  320 , and the electrode terminal  310 . The cap plate  350  may be a metal plate having a size and shape corresponding to the upper opening of the can  200 , and may include a predetermined size of terminal hole  352 , an electrolyte inlet port  354 , and a safety vent (not shown). 
     The electrolyte inlet port  354  is a hole through which an electrolyte for smoothly moving lithium ions is injected into the can  200  housing the electrode assembly  100 . After coupling the cap assembly  300  to the can  200 , the electrolyte may be injected through the electrolyte inlet port  354 , and the electrolyte inlet port  354  may be sealed with an electrolyte inlet port cap (not shown), thereby sealing the can  200 . 
     The terminal hole  352  is a hole through which the electrode terminal  310  is inserted. The terminal electrode  310  may be electrically connected to the terminal plate  330  disposed under the cap plate  350  through the terminal hole  352 . In order to insulate the electrode terminal  310  from the cap plate  350 , a gasket  360  formed of rubber or a non-conductive material having good insulating characteristics may be disposed at an outer side of the electrode terminal  310 . 
     The connection jig  410  may be fastened to the electrolyte inlet port  354  of the secondary battery to transmit the pressure in the secondary battery to the fluid filled in the pipe  430 . The connection jig  410  may include a main body  412  adhered to the electrolyte inlet port  354 , a projection  414  inserted into the electrolyte inlet port  354  of the secondary battery, and a sealing member  416  surrounding the projection  414  and sealing the electrolyte inlet port  354 . 
     The projection  414  may have a spiral cone shape to be readily inserted into the electrolyte inlet port  354 . In order to more precisely measure the internal pressure of the secondary battery based on external environments after sealing the electrolyte inlet port  354  with the electrolyte inlet port cap, the projection  414  may pierce through the electrolyte inlet port cap. 
     The projection  414  may have a length D 1  longer than a thickness of the cap plate D 2  of the secondary battery to readily measure the internal pressure of the secondary battery. Since the projection  414  may cause damage to the insulating case  320  and the electrode assembly  100  by being in contact with the insulating case  320  of the secondary battery, the projection  414  may have the length D 1  shorter than a distance D 3  between the electrolyte inlet port  354  and the insulating case  320 . 
     The pipe  430  may be filled with a pressure medium to measure the internal pressure of the secondary battery without discharging gas filled in the secondary battery and to transmit internal pressure variation of the secondary battery in real time. The pressure medium filled in the pipe  430  may be fluid such as oil. In consideration of factors, i.e., heat in both inside and outside of the secondary battery, the fluid may be a material that is not evaporated or pressure-reduced even above 400° C. 
     The pressure gauge  420  functions to display the internal pressure of the secondary battery transmitted by the pressure medium filled in the pipe  430 . The pressure gauge  420  may further include a fastening member  425  to control a fastening between the pressure gauge  420  and the pipe  430 . In order to measure the internal pressure of the secondary battery, the pressure medium, such as fluid in the pipe  430 , may need to be readily introduced or exchanged. Thus, after the fastening member  425  loosens the fastening of the pipe  430  and the pressure gauge  420 , air remaining in the pipe  430  may be discharged from between the pipe  430  and the pressure gauge  420  to facilitate filling of the pipe  430  with the pressure medium. The pressure medium may be introduced into the pipe  430  through the connection jig  410 . 
     The internal pressure measuring apparatus for a secondary battery in accordance with an exemplary embodiment of the present invention may include a storage medium  440  electrically connected to the pressure gauge  420  to record or store variation in internal pressure of the secondary battery, and may further include a display device  441  to display the variation in internal pressure of the secondary battery. 
     As described above, in the internal pressure measuring apparatus for a secondary battery in accordance with an exemplary embodiment of the present invention, the connection jig may be fastened to the electrolyte inlet port, and the pipe may be connected between the connection jig and the pressure gauge, so that may be possible to measure the internal pressure of the secondary battery as the internal pressure varies based on external environments in real time. 
     In addition, the pipe may be filled with a pressure medium such as fluid to measure the internal pressure of the secondary battery without discharging the gas filled in the secondary battery, thereby precisely measuring the internal pressure of the secondary battery. 
     As can be seen from the foregoing, since an internal pressure measuring apparatus for a secondary battery may measure the internal pressure of the secondary battery transmitted by a pressure medium such as fluid filled in a pipe connected between a pressure gauge and a connection jig fastened to an electrolyte inlet port, it may be possible to measure variation in internal pressure of the secondary battery in real time. 
     Exemplary embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.