Abstract:
A cylindrical lithium secondary battery including a winding-type electrode assembly having a first electrode plate to which a first electrode tap is attached, a second electrode plate to which a second electrode tap is attached, and a separator interposed between the first electrode plate and the second electrode plate. A space is formed through a central longitudinal axis of the electrode assembly. The battery includes a cylindrical case adapted to receive and house the electrode assembly, the cylindrical case having a bottom surface. A first insulation plate insulating the electrode assembly from the cylindrical case is located adjacent the bottom surface and includes a recess adapted to accommodate the first electrode tap, the first electrode tap being coupled to the bottom surface The battery also includes a cap assembly located at an opposite end of the cylindrical case from the bottom surface, the cap assembly being coupled to the second electrode tap and sealing the case.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0056422, filed on Jun. 28, 2005, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a cylindrical lithium ion secondary battery, and more particularly, to a cylindrical lithium secondary battery having improved structural stability. 
   2. Description of Related Art 
   Recently, a large number of compact and lightweight electronic apparatus such as cellular phones, notebook computers, and camcorders have been developed and manufactured. These portable electronic apparatus are provided with battery packs so that the apparatus can operate without separate power supplies. Each battery pack includes at least one battery to drive the portable electronic apparatuses for a predetermined time. 
   Recently, battery packs have employed secondary (rechargeable) rechargeable batteries. Representative secondary batteries include nickel cadmium (Ni—Cd) batteries, nickel hydride (Ni-MH) batteries, and lithium rechargeable batteries such as lithium (Li) polymer batteries and Lithium ion (Li-ion) batteries. 
   Lithium secondary batteries have an operating voltage of 3.6V which is three times higher than a Ni—Cd battery or a Ni-MH battery. In addition, lithium secondary batteries have a high energy density per unit weight. Therefore, demand for lithium secondary batteries has rapidly increased. 
   For lithium secondary batteries, a lithium-based oxide is used as a positive electrode active material and carbon is used as a negative electrode active material. In general, batteries are classified as either liquid electrolyte batteries or polymer electrolyte batteries according to the type of the electrolyte used. Lithium secondary batteries using liquid electrolyte are called lithium ion batteries, and lithium secondary batteries using polymer electrolyte are called lithium polymer batteries. Lithium secondary batteries are manufactured in various shapes and are classified, for example, into cylindrical batteries, prismatic batteries, and pouch-type batteries. 
   In general, a lithium secondary battery includes an electrode assembly, a case adapted to receive the electrode assembly, and electrolyte solution injected inside the case to enable the lithium ions to move. The electrode assembly includes a positive electrode plate coated with a positive electrode active material, a negative electrode plate coated with a negative electrode active material, and a separator interposed between the positive and negative electrode plates to prevent a short circuit between the two electrode plates and to allow only lithium ions to pass through. 
   The electrode assembly of a cylindrical lithium secondary battery is constructed by overlaying and rolling the positive electrode plate connected to a positive tab, the negative electrode plate connected to a negative tab, and the separator. 
   The electrode assembly is then inserted into the case and fixed therein. The electrolyte solution is injected into the case and the opening of the case is sealed with a cap assembly. Typically, insulation plates are combined with the electrode assembly, and the negative tab of the electrode assembly is attached to the cylindrical case. 
   The number of cylindrical lithium secondary batteries having high capacity is rapidly increasing. Accordingly, the positive and negative tabs of the electrode assembly have become thicker. 
   However, in a cylindrical lithium secondary battery, if the negative tab is thick, an insulation plate attached to the negative tab may become deformed so as to create a spatial non-uniformity in the battery. The non-uniformity may adversely affect the safety of the cylindrical lithium secondary battery when an external pressure is applied to the battery. 
   SUMMARY OF THE INVENTION 
   The present invention provides a cylindrical lithium secondary battery having an improved structural stability. More specifically, the cylindrical lithium secondary battery includes an insulation plate having a recession for receiving an electrode tab. 
   According to an aspect of the present invention, a cylindrical lithium secondary battery is provided including a winding-type electrode assembly comprising a first electrode plate to which a first electrode tab is attached, a second electrode plate to which a second electrode tab is attached, and a separator interposed between the first and second electrode plates, wherein a predetermined space is formed in a center of the electrode assembly; a cylindrical case comprising a cylindrical side surface having a predetermined space to receive the electrode assembly and a bottom surface of a lower portion of the cylindrical side surface; an insulation plate insulating the electrode assembly from the cylindrical case in the lower part of the electrode assembly and comprising a recession to receive one of the first and second electrode tabs; and a cap assembly combining into a top part of the case and sealing the top part of the case. 
   In addition, the insulation plate may be a circular-shaped flat plate and comprise a passing hole in a center portion. 
   In addition, a width of the recession may be equal to or larger than a diameter of the passing hole of the insulation plate. 
   In addition, a length of the recession is equal to or larger than a sum of radiuses of the insulation plate and the passing hole. 
   In addition, the cylindrical lithium secondary battery may further comprise a center pin inserted into a center space of the electrode assembly. 
   In addition, the cylindrical lithium secondary battery may further comprise an insulation plate of a top portion insulating the electrode assembly from the cap assembly in the top portion of the electrode assembly. 
   In addition, the cylindrical lithium secondary battery may further comprise electrolyte solution, which is inserted into the cylindrical case, enabling lithium ions to move. 
   According to another aspect of the present invention, there is provided a fabrication method of a cylindrical lithium secondary battery, comprising steps of: forming an electrode assembly having a predetermined space in a center by winding a first electrode plate to which a first electrode tab is attached, a second electrode plate to which a second electrode tab is attached, and a separator interposed between the first and second electrode plates; inserting the electrode assembly into a cylindrical case so that one of the first and second electrode tabs are received into a recession of an insulation plate comprising the recession in a bottom surface, and the insulation plate is disposed in a bottom portion; and combining a cap assembly into a top portion of the cylindrical case. 
   In addition, the fabrication method may further comprise a step of inserting an insulation of an upper portion insulating the electrode assembly from the cap assembly in the top portion of the electrode assembly. 
   In addition, the fabrication method may further comprise a step of inserting a center pin into a center space of the electrode assembly. 
   In addition, the fabrication method may further comprise a step of injecting electrolyte solution into the cylindrical case. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a perspective view of a cylindrical lithium secondary battery according to an embodiment of the present invention. 
       FIG. 1B  is a sectional view of the cylindrical lithium secondary battery  100  taken along section line A-A of  FIG. 1 . 
       FIG. 1C  is a sectional view of the cylindrical lithium secondary battery  100  taken along section line B-B of  FIG. 1 . 
       FIG. 2A  is a top view of the cylindrical lithium secondary battery according to an embodiment of the present invention. 
       FIG. 2B  is a diagram of a lower insulation plate and an electrode tab of a cylindrical lithium secondary battery according to an embodiment of the present invention. 
       FIG. 3  is a flowchart of a fabrication method of the cylindrical lithium second battery according to another embodiment of the present invention. 
       FIGS. 4A to 4D  are diagrams illustrating a fabrication method of the cylindrical lithium second battery according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As illustrated in  FIGS. 1A to 1C , a cylindrical lithium secondary battery  100  according to an embodiment of the present invention has a structure including an electrode assembly  200  generating a voltage difference between charging and discharging, a cylindrical case  300  accommodating the electrode assembly  200 , a cap assembly  400  assembled onto the cylindrical case  300  to contain the electrode assembly  200 , electrolyte solution injected inside the cylindrical case  300  to enable the lithium ions to move, and a center pin  600  disposed in the electrode assembly  200 . 
   The electrode assembly  200  includes a first electrode plate  210  coated with, for example, a positive electrode material, and a second electrode plate  220  coated with, for example, a negative active material, and a separator  230  interposed between the first and second electrode plates  210 ,  220  to prevent a short circuit between the two electrode plates  210 ,  220  and to allow only lithium ions (Li-ions) to pass through. The first and second electrode plates  210 ,  220  and the separator  230  are wound in a substantially circular form and are inserted into the cylindrical case  300 . In addition, a first electrode tab  215 , typically made from aluminum and protruding from the electrode assembly may function as a positive electrode tab and may be attached to the first electrode plate  210 . In addition, a second electrode tab  225 , typically made from nickel and protruding from the electrode assembly may function as a negative electrode tab and may be attached to the second electrode plate  220 . However, materials of the electrode tabs are not limited thereto. In addition, upper and lower insulation plates  241 ,  245  are attached to the electrode assembly to prevent direct contact between the electrode assembly and the cap assembly  400  and electrode assembly and the cylindrical case  300 . 
   As shown in  FIG. 2B , a recess for receiving the second electrode tab  225  functioning as the negative tab is formed in an exterior facing surface of the lower insulation plate  245 . 
   The cylindrical case  300  includes a space into which the electrode assembly  200  is receivable. The cylindrical case  300  includes a cylindrical surface  310  and a bottom surface  320 . An end of the cylindrical case  300  is open to allow insertion of the electrode assembly  200 . The second electrode tab  225  may be attached to the bottom surface  320  of the cylindrical case  300  to allow the case to functions as a negative electrode terminal. The cylindrical case  300  may be made of, for example, aluminum, iron, or an alloy of aluminum and iron. The cylindrical case  300  includes a crimping region  330  and a beading region  340  to more securely fix the cap assembly to the cylindrical case  300 . 
   The cap assembly  400  includes a conductive safety bent  410 , a printed circuit board (PCB)  420 , a positive thermistor  430 , a conductive electrode cap  440 , and an insulation gasket  450 . The conductive safety bent  410  to which the first electrode tab  215  is welded is inverted when the battery is overcharged or when the battery generates an excessive amount of heat. The PCB  420  is electrically and mechanically connected to the conductive safety bent  410 . The connection between the PCB  420  and the conductive safety bent  410  is severed when the conductive safety bent  410  is inverted. The positive thermistor  430  is connected to the PCB and cuts off at a temperature above a predetermined temperature. The conductive electrode cap  440  is electrically and mechanically connected to the positive thermistor  430  and provides a current to an external circuit. The insulation gasket  450  has a form wrapping around the conductive safety bent  410 , the PCB  420 , the positive thermistor  430 , and the electrode cap  440  and insulates these components from the cylindrical case  300 . In one exemplary embodiment, the electrode cap  440  is attached to the first electrode tab  215  and functions as a positive electrode terminal. 
   Electrolyte solution  500  is injected into the cylindrical case  300  to enable the lithium ions to move between the electrode assembly  200  and the case  300 . The electrolyte solution  500  functions as a carrier of the lithium ions generated by an electro-chemical reaction during charging or discharging in positive and negative electrodes inside the battery. The electrolyte solution  500  may be an organic electrolyte solution which is a mixture of a lithium salt and a high-purity organic solvent. Alternatively, the electrolyte solution may be a polymer using polymer electrolyte. However, the type of the electrolyte solution  500  is not limited thereto. 
   The winding core member  600  is inserted into a central space of the winding electrode assembly  200  and prevents the winding electrode assembly  200  from relaxing and uncoiling. In addition, the winding core member  600  serves to prevent the winding electrode assembly  200  from being deformed by an external force. The winding core member  600  is formed in a substantially tubular form. 
   In addition, the winding core member  600  is formed to have a height of between about 90% to 110% of a height of the electrode assembly  200 , and a lower end of the winding core member  600  is disposed on the second electrode tab  225 . If the height of the winding core member  600  is less than 90% of the height of the electrode assembly  200 , the electrode assembly  200  may not be able to be securely attached to the winding core member. If the height of the winding core member  600  is greater than 110% the height of the electrode assembly  200 , the winding core member  600  may contact and interfere with the cap assembly  400 . 
   Referring to  FIGS. 2A and 2B , the lower insulation plate  245  of the cylindrical lithium secondary battery  100  is formed in a substantially circular flat plate shape. 
   The lower insulation plate  245  includes a centrally located substantially circular-shaped through-hole  245   a  and a recess  245   b  formed in an exterior facing surface of the lower insulation plate. The recess  245   b  is adapted to receive the second electrode tab  225  functioning as a negative electrode tab. The hole  245   a  functions as a pathway allowing the winding core member  600  to be connected to the second electrode tab  225 . 
   A width W of the recess  245   b  may be equal to or larger than a diameter 2d 1  of the hole, and a length L of the recess  245   b  may be equal to or larger than a sum of a radius d 2  of the lower insulation plate  245  and a radius d 1  of the hole. 
   In addition, as illustrated in  FIG. 2B , the second electrode tab  225  is received in the recess  245   b  and is attached to a bottom surface of the cylindrical case  300   
   According to the above-described structure, the likelihood of deformity of the lower insulation plate  245  is reduced, stabilizing and improving a structure of the cylindrical lithium secondary battery. 
   Referring to  FIG. 3 , a fabrication method of the cylindrical lithium second battery according to an embodiment of the present invention includes forming (S 1 ) an electrode assembly  200 , inserting (S 2 ) a lower insulation plate and an electrode assembly into a case, inserting (S 3 ) a center pin axially through the center of the electrode assembly, injecting (S 4 ) electrolyte solution into the case, and combining (S 5 ) a cap assembly with the case to complete the cylindrical lithium secondary battery. 
   Referring now to  FIG. 3  and  FIGS. 4A-4D , a method for assembling a cylindrical lithium secondary battery according to an embodiment of the present invention will be described. With reference to  FIG. 4A , a first electrode plate  210 , a separator  230 , and a second electrode plate  220  are layered. A winding axis  700  is attached to one end of the layered structure, and the layered structure is wound into a substantially cylindrical shape to form the electrode assembly. Before the electrode plates  210 ,  230  and the separator  220  are wound, first and second electrode tabs  215 ,  225  may be attached to first and second electrode plates  210 ,  220 , respectively. 
   Referring to  FIG. 4B , the second electrode tab  225  is folded into the recess  245   b  of the lower insulation plate  245  and the lower insulation plate  245  and the electrode assembly  200  are inserted to the cylindrical case  300 . The second electrode tab  225  may be attached to the recess  245   b  by, for example, welding. 
   The winding axis  700  may be removed from the electrode assembly  200  before the electrode assembly  200  is inserted into the case  300 . 
   Referring to  FIG. 4C , a center pin  600  is inserted into a space vacated by removal of the winding axis  700 . Additionally, the second electrode tab  225  may be fixed to the bottom surface  320  of the cylindrical case  300  by, for example, welding, before the winding core member  600  is inserted. Accordingly, the winding core member  600  is disposed to contact the second electrode tab  225  and allows the second electrode tab  225  to be more securely in contact with the cylindrical case. 
   With continued reference to  FIG. 4C , electrolyte solution  500  is injected to the case  300  after the electrode assembly  200  has been inserted into the case. The electrolyte solution  500  enables the lithium ions to move between the first and second electrode plates  210 ,  220  during charging or discharging of the battery. 
   Referring to  FIG. 4D , the cap assembly  400  is combined with the cylindrical case  300  to complete fabrication of the cylindrical lithium secondary battery  100 , securing the electrode assembly  200 , the winding core member  600 , the winding core member  600 , and the electrolyte solution  500  in the case  300 . 
   More specifically, a substantially ring-shaped insulation gasket  450  is inserted into a top portion of the cylindrical case  300 , and the first electrode tab  215 , a conductive safety bent  410 , a printing circuit board  420 , and a positive thermistor  430 , and an electrode cap  440  are sequentially located within the gasket. 
   Thereafter, a portion of the cylindrical case  300  is beaded to form a beading region  340  and a portion of the case  300  is crimped to form a crimping region  300 , reducing the likelihood that the cap assembly  400  will be detached from the case  300 . 
   As described above, in the cylindrical lithium secondary battery according to embodiments of the present invention, the likelihood of deformity of a lower insulation plate resulting from a thick electrode tab may be reduced. More specifically, a lower insulation plate having a recess adapted to receive an electrode tab is provided. Accordingly, a stability of the cylindrical lithium secondary battery is improved. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.