Abstract:
An electrode assembly for a secondary battery having a positive and negative electrode plates with a separator interposed therebetween. The positive and negative electrode plates have coated and uncoated portions. The length of the interconnection between the coated and uncoated portion of the positive electrode plate is greater than the length of the interconnection between the coated and uncoated portions of the negative electrode plate to reduce heat concentration occurring at the positive electrode plate. In one implementation, that relative lengths between the boundary intervals between the coated and uncoated portions of the positive and negative electrodes are determined using a ratio comprised of the product of the relative resistances and thicknesses.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/430,893 filed Jan. 7, 2011, which is hereby incorporated by reference in its entirety herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    One or more embodiments of the present invention relate to a secondary battery, and more particularly, to a structure of a secondary battery. 
         [0004]    2. Description of Related Art 
         [0005]    Recently, compact and light portable electric/electronic devices such as cellular phones, notebook computers, and camcorders have been actively developed and produced. Thus, a portable electric/electronic device includes a battery pack so as to be able to operate in any place without a separate power source. The battery pack includes a rechargeable secondary battery, in consideration of economical aspects. Examples of a representative secondary battery are a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni-MH) battery, a lithium (Li) battery, and a lithium (Li)-ion battery. In particular, the Li-ion battery has an operating voltage that is about three times higher than those of the Ni—Cd battery and the Ni-MH battery, which have been widely used as power sources of portable electronic devices. In addition, the Li-ion battery has been widely used due to having a high energy density per specific weight. A secondary battery uses a Li-based oxide as a positive active material, and uses a carbon material as a negative active material. 
       SUMMARY OF THE INVENTION 
       [0006]    One or more embodiments of the present invention include a secondary battery. 
         [0007]    According to one or more embodiments of the present invention, the aforementioned needs are satisfied by an electrode assembly comprising a first electrode plate having a first uncoated portion and a first coated portion that is coated with a first electrode material and a second electrode plate having a second uncoated portion and a second coated portion that is coated with a second electrode material. In this embodiment, the invention further includes a separator interposed between the first electrode plate and the second electrode plate; wherein a first length between the first uncoated portion and the first coated portion is greater than a second length between the second uncoated portion and the second coated portion. 
         [0008]    In another embodiment of the present invention, the aforementioned needs are satisfied by a method of fabricating an electrode assembly for a rechargeable battery, the method comprising forming a first electrode plate having a first uncoated portion and a first coated portion that is coated with a first electrode material, forming a second electrode plate having a second uncoated portion and a second coated portion that is coated with a second electrode material. In this embodiment, the invention further comprises sizing the length of the boundary interval between the uncoated portion and the coated portion of the first electrode plate and the length of the boundary interval between the uncoated portion and the coated portion of the second electrode plate based upon the heat produced by the current flow through the boundary intervals in the first and second electrode plates so that the heat produced by the flow of current through the first boundary interval is reduced as a result of increasing the length of the first boundary interval. In this embodiment, the invention further comprises assembling the first electrode plate with the second electrode plate with a separator interposed therebetween. 
         [0009]    In yet another embodiment the aforementioned needs are satisfied by a battery assembly comprising a first electrode plate having a first uncoated portion and a first coated portion that is coated with a first electrode material, and a second electrode plate having a second uncoated portion and a second coated portion that is coated with a second electrode material. In this embodiment the invention further comprises a separator interposed between the first electrode plate and the second electrode plate; wherein a first length between the first uncoated portion and the first coated portion is greater than a second length between the second uncoated portion and the second coated portion. In this embodiment, the invention comprises a case that receives the first electrode plate, the second electrode plate and the separator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded perspective view of a lithium ion polymer battery, according to an embodiment of the present invention; 
           [0011]      FIG. 2  is an exploded perspective view of an electrode assembly of  FIG. 1 ; 
           [0012]      FIG. 3  is an image showing a temperature distribution of a positive electrode plate after discharge has ended, according to an embodiment of the present invention; 
           [0013]      FIG. 4A  is an enlarged perspective view of a portion ‘IVa’ of  FIG. 2 ; 
           [0014]      FIG. 4B  is an enlarged perspective view of a portion ‘IVb’ of  FIG. 2 ; 
           [0015]      FIG. 5  is a plan view of an electrode assembly viewed from above, according to a modified embodiment of the electrode assembly of  FIG. 2 ; and 
           [0016]      FIG. 6  is perspective view of a positive electrode plate, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. 
         [0018]    One or more embodiments of the present invention include a secondary battery that is configured as any of various types. For example, the secondary battery may be a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni-MH) battery, or a lithium (Li) battery. The lithium secondary battery may be, for example, a lithium metal battery using a liquid electrolyte, a lithium ion battery, or a lithium polymer battery using a high-molecular weight solid electrolyte. The lithium polymer battery may be classified as a complete solid-type lithium polymer battery that does not contain an organic electrolyte, or a lithium ion polymer battery  1  that uses a gel-type high-molecular weight electrolyte, according to a type of a high-molecular solid electrolyte. Hereinafter, a structure of a secondary battery will be described in terms of the lithium ion polymer battery  1 , but is not limited thereto, and thus secondary batteries of various types may be used. 
         [0019]    With reference to  FIGS. 1 and 2 , a structure of the lithium ion polymer battery  1  will be described.  FIG. 1  is an exploded perspective view of the lithium ion polymer battery  1 , according to an embodiment of the present invention.  FIG. 2  is an exploded perspective view of an electrode assembly  100  of  FIG. 2 . The lithium ion polymer battery  1  may include the electrode assembly  100 , a case  200 , and an electrolyte (not shown). 
         [0020]    The electrode assembly  100  may include a positive electrode plate  110 , a negative electrode plate  120 , and a separator  130 . The electrode assembly  100  may be formed by sequentially stacking the positive electrode plate  110  and the negative electrode plate  120 . A separator  130  may be interposed between the positive electrode plate  110  and the negative electrode plate  120 . The positive electrode plate  110  may include a positive electrode material  111 , a positive electrode non-coated portion  111   a , and a positive active material  112 . The positive electrode material  111  may include, for example, aluminum (Al). A portion of the positive electrode material  111  may extend to form the positive electrode non-coated portion  111   a . The positive active material  112  may include a typical active material. For example, the positive active material  112  may include a lithium cobalt oxide (LiCoO 2 ), but is not limited thereto. That is, the positive active material  112  may include a silicon-based material, a tin-based material, an aluminum-based material, a germanium-based material, or the like. In this case, the positive active material  112  may include a lithium titanium oxide (LTO), in addition to a typical active material. Referring to  FIG. 1 , the positive electrode non-coated portion  111   a  may be connected to a positive electrode lead tap  115  connected to an external terminal of the case  200 . 
         [0021]    The negative electrode plate  120  may include a negative electrode material  121 , a negative electrode non-coated portion  121   a , and a negative active material  122 . The negative electrode material  121  may include, for example, copper (Cu). A portion of the negative electrode material  121  may extend to form the negative electrode non-coated portion  121   a . The negative active material  122  may include a typical active material. For example, the negative active material  122  may include graphite. Referring to  FIG. 1 , the negative electrode non-coated portion  121   a  may be connected to a negative electrode lead tap  125  connected to an external terminal of the case  200 . 
         [0022]    The case  200  may accommodate the electrode assembly  100  and the electrolyte (not shown). The case  200  may be a flexible pouch case. 
         [0023]      FIG. 3  is an image showing a temperature distribution of a positive electrode plate  101  after discharge has ended, according to an embodiment of the present invention. Referring to  FIG. 3 , it may be known that temperatures of a first positive electrode plate portion P 1  corresponding to the positive active material  112 , and a second positive electrode plate portion P 2  extending from the first positive electrode plate portion P 1 , are different. In this case, the reference numerals P 1  and P 2  may correspond to the reference numerals  111  and  111   a  of  FIG. 2 , respectively. With regard to a temperature distribution of a central portion M of the first positive electrode plate portion P 1 , a minimum temperature is 38.4° C., a maximum temperature is 41.3° C., and an average temperature is 39.6° C., as shown in  FIG. 3 . A temperature of a point in the central portion M is 40.0° C., as shown in  FIG. 3 . On the other hand, a temperature of a boundary portion (B) between the first positive electrode plate portion P 1  and the second positive electrode plate portion P 2  is 45.1° C. That is, the temperature of the boundary portion (B) between the first positive electrode plate portion P 1  and the second positive electrode plate portion P 2  is higher than points such as those of the central portion M. It may be known that a temperature is increased at a point corresponding to a boundary portion between the positive active material  112  and the positive electrode non-coated portion  111   a . A temperature is actively increased in the boundary portion (B) in the positive electrode plates  101  and  110 , compared to the negative electrode plate  120 . This is because, since a resistance value of the positive active material  112  is generally high, heat is generated at the boundary portion (B) between the positive active material  112  and the positive electrode material  111  due to Joule&#39;s heating. The more heat generated between the positive active material  112  and the positive electrode material  111 , the higher a current value of C-rate. Such heat intensifies deterioration of a battery as charge/discharge are repeatedly performed, thereby reducing the lifetime and stability of the battery. Thus, it is required to minimize such deterioration. 
         [0024]    With reference to  FIGS. 4A ,  4 B, and  5 , a positive electrode boundary interval w 1  between the positive active material  112  and the positive electrode non-coated portion  111   a , and a negative electrode boundary interval w 2  between the negative active material  122  and the negative electrode non-coated portion  121   a  will be described.  FIG. 4A  is an enlarged perspective view of a portion ‘IVa’ of  FIG. 2 .  FIG. 4B  is an enlarged perspective view of a portion ‘IVb’ of  FIG. 2 .  FIG. 5  is a plan view of an electrode assembly  100  viewed from above, according to a modified embodiment of the electrode assembly  100  of  FIG. 2 . 
         [0025]    Comparing the positive electrode plate  110  and the negative electrode plate  120 , since the negative active material  122  of the negative electrode plate  120  uses a material with a low resistance value, such as graphite, a resistance difference between the negative active material  122  and the negative electrode non-coated portion  121   a  including Cu or the like may not be great, but a resistance difference between the positive active material  112  with a high resistance value and the positive electrode non-coated portion  111   a  may be great. 
         [0026]    In this case, the positive electrode boundary interval w 1  is defined as an interval between the positive active material  112  and the positive electrode non-coated portion  111   a , and the negative electrode boundary interval w 2  is defined as an interval between the negative active material  122  and the negative electrode non-coated portion  121   a . A current is passed through the positive electrode non-coated portion  111   a , the negative electrode non-coated portion  121   a , and the like through charge/discharge, and heat is generated between the positive active material  112  and the positive electrode non-coated portion  111   a , and between the negative active material  122  and the negative electrode non-coated portion  121   a , due to Joule&#39;s heating. In this case, the amount heat generated due to Joule&#39;s heating is affected by the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2 . Thus, the positive electrode boundary interval w 1 , which generates a large amount of heat due to having a high resistance value associated therewith, may be wider than the negative electrode boundary interval w 2 . In this case,  FIG. 5  is a plan view of the electrode assembly  100 , in which the positive electrode boundary interval w 1  is wider than the negative electrode boundary interval w 2 , viewed from above. The positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  will be described in more detail, with reference to equations. 
         [0027]    When a capacity C of each unit electrode plate is obtained by dividing the entire capacity of the lithium ion polymer battery  1  by the number of positive electrode plates  110  and negative electrode plates  120 , a current density of unit area of the positive electrode plate  110  or the negative electrode plate  120  may be obtained by dividing the capacity C by a unit area. For example, in  FIG. 4A , when a capacity of the positive electrode plate  110  is C, a current density of unit area (mA/mm 2 ) of a boundary portion between the positive active material  112  and the positive electrode non-coated portion  111   a  may be obtained by C/w 1 d 1 . Similarly, in  FIG. 4B , when a capacity of the negative electrode plate  120  is C, a current density of unit area (mA/mm 2 ) of a boundary portion between the negative active material  122  and the negative electrode non-coated portion  121   a  may be obtained by C/w 2 d 2 . In this case, d 1  is a thickness of the positive electrode plate  110 , and d 2  is a thickness of the negative electrode plate  120 . 
         [0028]    In this case, a heat amount Q generated per unit area may be calculated according to Equation 1 below 
         [0000]        Q=I   2   Rt (J)  (1)
 
         [0029]    In Equation 1, I is a current density of unit area (mA/mm 2 ), R is a resistance value (Ω), and t is a period of time (sec). A heat amount Q 1  per unit area of the positive electrode plate  110  is 
         [0000]    
       
         
           
             
               
                 ( 
                 
                   C 
                   
                     
                       w 
                       1 
                     
                      
                     
                       d 
                       1 
                     
                   
                 
                 ) 
               
               2 
             
              
             
               R 
               1 
             
              
             
               t 
               . 
             
           
         
       
     
         [0000]    In this case, R 1  is a resistance value between the positive active material  112  and the positive electrode material  111 . A heat amount (Q 2 ) per unit area of the negative electrode plate  120  is 
         [0000]    
       
         
           
             
               
                 ( 
                 
                   C 
                   
                     
                       w 
                       2 
                     
                      
                     
                       d 
                       2 
                     
                   
                 
                 ) 
               
               2 
             
              
             
               R 
               2 
             
              
             
               t 
               . 
             
           
         
       
     
         [0000]    In this case, R 2  is a resistance value between the negative active material  122  and the negative electrode material  121 . 
         [0030]    In general, the resistance R 1  between the positive active material  112  and the positive electrode material  111  is greater than the resistance R 2  between the negative active material  122  and the negative electrode material  121 . Thus, in boundary portions between the positive active material  112 / the negative active material  122  and the positive electrode non-coated portion  111   a / the negative electrode non-coated portion  121   a , the heat amount Q 1  per unit area of the positive electrode plate  110  is greater than the heat amount Q 2  per unit area of the negative electrode plate  120 , and thus the positive electrode plate  110  may deteriorate and thus may be damaged. 
         [0031]    In general, a difference between the thickness d 1  of the positive electrode plate  110  and the thickness d 2  of the negative electrode plate  120  is not that great. Since it is not easy to design-change the resistances R 1  and R 2  the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may be controlled so that heat generated at a boundary portion of the positive electrode plate  110  may be less than or equal to heat generated at a boundary portion of the negative electrode plate  120 . 
         [0032]    According to Equations 2 and 3, the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may be calculated to be such that the heat amount Q 1  per unit area of the positive electrode plate  110  is equal to the heat amount Q 2  per unit area of the negative electrode plate  120 . 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           C 
                           
                             
                               w 
                               1 
                             
                              
                             
                               d 
                               1 
                             
                           
                         
                         ) 
                       
                       2 
                     
                      
                     
                       R 
                       1 
                     
                      
                     t 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           C 
                           
                             
                               w 
                               2 
                             
                              
                             
                               d 
                               2 
                             
                           
                         
                         ) 
                       
                       2 
                     
                      
                     
                       R 
                       2 
                     
                      
                     t 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     w 
                     1 
                   
                   = 
                   
                     
                       
                         
                           
                             R 
                             1 
                           
                           
                             R 
                             2 
                           
                         
                       
                       · 
                       
                         
                           d 
                           2 
                         
                         
                           d 
                           1 
                         
                       
                     
                      
                     
                       w 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0033]    That is, when the heat amount Q 1  per unit area of the positive electrode plate  110  is equal to the heat amount Q 2  per unit area of the negative electrode plate  120 , according to Equation 2, the positive electrode boundary interval w 1  may be expressed using the negative electrode boundary interval w 2  and constants, according to Equation 3. 
         [0034]    Thus, when the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  satisfy Equation 3, heat may be uniformly generated at the boundary portions of the positive electrode plate  110  and the negative electrode plate  120  rather than being generated more at one side. 
         [0035]    Hereinafter, the heat amount Q 1  per unit area of the positive electrode plate  110  and the heat amount Q 2  per unit area of the negative electrode plate  120  according to the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  will be described. The positive electrode material  111  may include Al, and a resistance value of Al may be about 0.3Ω. A surface resistance value of the positive active material  112  may be about 620Ω. In this case, a resistance value between the positive electrode material  111  and the positive active material  112  may be about 300Ω. A thickness of the positive electrode material  111  may be about 20 μm. 
         [0036]    In addition, the negative electrode material  121  may include Cu, and a resistance value of Cu may be about 0.3Ω. A surface resistance value of the negative active material  122  may be about 2.8Ω. A resistance value between the negative electrode material  121  and the negative active material  122  may be about 1.3Ω. A thickness of the negative electrode material  121  may be about 15 μm. In this case, by substituting the values into the constants of Equation 3, the following result may be obtained according to Equation 4. 
         [0000]    
       
         
           
             
               
                 
                   
                     w 
                     1 
                   
                   = 
                   
                     
                       
                         
                           
                             300 
                             1.3 
                           
                         
                         · 
                         
                           20 
                           15 
                         
                       
                        
                       
                         w 
                         2 
                       
                     
                     = 
                     
                       11.39 
                        
                       
                           
                       
                        
                       
                         w 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0037]    That is, when the negative electrode boundary interval w 2  is 8.8% of the positive electrode boundary interval w 1  (w 2 /w 1 ), the heat amount Q 1  per unit area of the positive electrode plate  110  may be equal to the heat amount Q 2  per unit area of the negative electrode plate  120 . Referring to  FIG. 5 , the sum of the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may not be greater than an entire width A of the positive electrode plate  110  and the negative electrode plate  120 . If not, the positive electrode non-coated portion  111   a  may overlap the negative electrode non-coated portion  121   a  and thus may cause a short circuit. Thus, when the positive electrode non-coated portion  111   a  and the negative electrode non-coated portion  121   a  are maximally enlarged, that is, when the sum of the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  is equal to the width A of the positive electrode plate  110  and the negative electrode plate  120 , the positive electrode boundary interval w 1  may be enlarged to a maximum of 92% (11.39/12.39) of the entire width A of the positive electrode plate  110  and the negative electrode plate  120 . 
         [0038]    If the sum of the positive electrode non-coated portion  111   a  and the negative electrode non-coated portion  121   a  is equal to entire width A of the positive electrode plate  110  and the negative electrode plate  120 , the positive electrode boundary interval w 1  needs to be equal to or greater than the negative electrode boundary interval w 2 , and thus the positive electrode boundary interval w 1  may be 50 to 92% of the entire width A of the positive electrode plate  110  and the negative electrode plate  120 . 
         [0039]    In addition, as the positive electrode boundary interval w 1  is enlarged, a contact area between the positive electrode lead tap  115  and the positive electrode non-coated portion  111   a  is further increased, and a resistance value between the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115  may also be reduced. That is, the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115  are electrically connected, and thus resistance is present between the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115 . Since a contact area between the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115  is enlarged, resistance between the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115  is reduced. Thus, heat generated due to the resistance between the positive electrode non-coated portion  111   a  and the positive electrode lead tap  115  may be reduced. 
         [0040]    The heat amount Q 1  per unit area of the positive electrode plate  110  and the heat amount Q 2  per unit area of the negative electrode plate  120  are calculated as follows. The electrode assembly  100  may include 42 pairs of positive electrode plates  110  and negative electrode plates  120 . In detail, the electrode assembly  100  includes the 42 pairs of positive electrode plates  110  and negative electrode plates  120 , wherein a single negative electrode plate  120  and a single positive electrode plate  110  corresponding thereto may constitute each pair, and may further include a negative electrode plate  120  corresponding to the outermost positive electrode  110 . That is, the 43 negative electrode plates  120  and the 42 positive electrode plates  110  may be alternatingly disposed. In this case, the number of negative electrode plates  120  and the number of positive electrode plates  110  are just examples, and are not particularly limited. 
         [0041]    In this case, an area of the positive electrode plates  110  or the negative electrode plates  120  may be about 540 cm 2 . A current density of the lithium ion polymer battery  1  may be 1.25 mA/cm 2 . A capacity of a single lithium ion polymer battery  1  according to a current capacity per unit weight of an active material of a unit cell may be about 56.98 A. Thus, a capacity per sheet of the positive electrode plate  110  the negative electrode plate  120 , obtained by dividing the capacity of the lithium ion polymer battery  1  by 42, may be about 1357 mA. 
         [0042]    Table 1 shows a heat amount according to the positive electrode boundary interval w 1 . Referring to  FIGS. 2 and 4A , when a reference corresponds to a case where an entire width of the positive electrode plate  110  is about 245 mm, and the positive electrode boundary interval w 1  is 90 mm, the heat amount Q 1  per unit area of the positive electrode plate  110  is obtained. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Positive electrode boundary 
                 130% 
                 120% 
                 110% 
                 100% 
                  90% 
                  80% 
               
               
                 interval ratio (%) 
               
               
                 Positive electrode boundary 
                 117 
                 108 
                 99 
                 90 
                 81 
                 72 
               
               
                 interval w 1 (mm) 
               
               
                 Positive material boundary 
                 2.34 
                 2.2 
                 2.0 
                 1.8 
                 1.6 
                 1.4 
               
               
                 sectional area (mm 2 ) 
               
               
                 Current density per unit 
                 579.8 
                 628.1 
                 685.2 
                 753.7 
                 837.4 
                 942.1 
               
               
                 area (mA/mm 2 ) 
               
               
                 Heat amount Q1 per unit 
                 101 
                 118 
                 141 
                 170 
                 210 
                 266 
               
               
                 area of positive electrode 
               
               
                 plate (J) 
               
               
                 Increase and decrease with 
                  59% 
                  69% 
                  83% 
                 100% 
                 123% 
                 156% 
               
               
                 respect to reference 
               
               
                   
               
             
          
         
       
     
         [0043]    In  FIG. 1 , a sectional area of a positive electrode material boundary is a value obtained by multiplying the positive electrode boundary interval w 1  by the thickness d 1  of the positive electrode material  111 . A current density of unit area is a value obtained by dividing a capacity of each sheet of the positive electrode plate  110  of 1357 mA by the sectional area of the positive electrode material boundary. The heat amount Q 1  per unit area of the positive electrode plate  110  is obtained by obtaining a value based on Equation 1 and then multiplying the value by 10 6 . 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 Negative electrode boundary interval ratio (%) 
               
             
          
           
               
                   
                 100% 
                 90% 
                 80% 
                 70% 
                 60% 
               
               
                   
               
               
                 Negative 
                 90 
                 81 
                 72 
                 63 
                 54 
               
               
                 electrode 
               
               
                 boundary 
               
               
                 interval w 2  (mm) 
               
               
                 Negative 
                 1.35 
                 1.215 
                 1.08 
                 0.945 
                 0.81 
               
               
                 material 
               
               
                 boundary 
               
               
                 sectional area 
               
               
                 (mm 2 ) 
               
               
                 Current density 
                 1004.938 
                 1116.598 
                 1256.481 
                 1435.979 
                 1675.309 
               
               
                 per unit area 
               
               
                 (mA/mm 2 ) 
               
               
                 Heat amount 
                 1.312871 
                 1.620829 
                 2.052369 
                 2.680646 
                 3.648657 
               
               
                 Q2 per unit 
               
               
                 area of 
               
               
                 negative 
               
               
                 electrode plate 
               
               
                 (J) 
               
               
                 Increase and 
                 100% 
                 123% 
                 156% 
                 204% 
                 278% 
               
               
                 decrease with 
               
               
                 respect to 
               
               
                 reference 
               
               
                   
               
             
          
           
               
                   
                 Negative electrode boundary interval ratio (%) 
               
             
          
           
               
                   
                 50% 
                 40% 
                 30% 
                 20% 
                 10% 
                 8.8% 
               
               
                   
               
               
                 Negative 
                 45 
                 36 
                 27 
                 18 
                 9 
                 7.92 
               
               
                 electrode 
               
               
                 boundary 
               
               
                 interval 
               
               
                 w 2  (mm) 
               
               
                 Negative 
                 0.675 
                 0.54 
                 0.405 
                 0.27 
                 0.135 
                 0.1188 
               
               
                 material 
               
               
                 boundary 
               
               
                 sectional 
               
               
                 area (mm 2 ) 
               
               
                 Current 
                 2010.37 
                 2512.963 
                 3350.62 
                 5025.926 
                 10051.85 
                 11422.56 
               
               
                 density 
               
               
                 per unit 
               
               
                 area 
               
               
                 (mA/mm 2 ) 
               
               
                 Heat 
                 5.254066 
                 8.209478 
                 14.5946 
                 32.83791 
                 131.3516 
                 169.53 
               
               
                 amount 
               
               
                 Q2 per 
               
               
                 unit area 
               
               
                 of 
               
               
                 negative 
               
               
                 electrode 
               
               
                 plate (J) 
               
               
                 Increase 
                 400% 
                 625% 
                 1112% 
                 2501% 
                 10005% 
                 12913% 
               
               
                 and 
               
               
                 decrease 
               
               
                 with 
               
               
                 respect 
               
               
                 to 
               
               
                 reference 
               
               
                   
               
             
          
         
       
     
         [0044]    Values of Table 2 may be obtained by using a method similar to that of Table 1. In this case, a positive/negative electrode boundary interval ratio (%) refers to a degree of increase and decrease with respect to a reference based on a case where the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  are each 90 mm. The increase and decrease with respect to the reference refers to increase and decrease in a heat amount based on a case where the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  are each 90 m m. In this case, the widths of the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may be determined in consideration of the sum of the heat amount Q 1  per unit area of the positive electrode plate  110  and the heat amount Q 2  per unit area of the negative electrode plate  120 . For example, when the negative electrode boundary interval w 2  (mm) is 9 mm, the heat amount Q 2  (J) per unit area of the negative electrode plate  120  may be about 131 J, and a width of the negative electrode boundary interval w 2  may be determined to be within 99 to 108 mm so that the heat amount Q 1  (J) per unit area of the positive electrode plate  110  may be equal to the heat amount Q 2  per unit area of the negative electrode plate  120 . 
         [0045]    Referring to Table 1, when the positive electrode boundary interval ratio is 100%, the heat amount Q 1  per unit area of the positive electrode plate  110  is about 170 (J). Referring to Table 2, when the negative electrode boundary interval ratio is 8.8%, the heat amount Q 2  per unit area of the negative electrode plate  120  is about 169.53 (J). Likewise, when the heat amount Q 1  per unit area of the positive electrode plate  110  is similar to the heat amount Q 2  per unit area of the negative electrode plate  120 , deterioration of a battery due to non-uniform heat amount may be reduced. If a temperature is partially increased due to a non-uniform heat amount, the lifetime of the battery may be reduced. For example, a solid electrolyte interface (SEI) layer disposed in the battery is a protective layer for facilitating stable charge/discharge of an electrolyte, and may be weak to heat and thus damaged at a temperature of about 60 to about 80° C. Thus, if heat amounts are uniform, the SEI layer and the like may not be damaged due to a non-uniform heat amount, thereby ensuring the stability and lifetime of the battery. 
         [0046]    In this case, it is obviously that the combination of the heat amount Q 1  per unit area of the positive electrode plate  110  and the heat amount Q 2  per unit area of the negative electrode plate  120  has various forms. This is generalized in Equation 5 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     F 
                      
                     
                       ( 
                       
                         
                           w 
                           1 
                         
                         , 
                         
                           w 
                           2 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           ( 
                           
                             C 
                             
                               
                                 w 
                                 1 
                               
                                
                               
                                 d 
                                 1 
                               
                             
                           
                           ) 
                         
                         2 
                       
                        
                       
                         R 
                         1 
                       
                        
                       t 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             C 
                             
                               
                                 w 
                                 2 
                               
                                
                               
                                 d 
                                 2 
                               
                             
                           
                           ) 
                         
                         2 
                       
                        
                       
                         R 
                         2 
                       
                        
                       t 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0047]    In this case, the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  for minimizing a function F(w 1 ,w 2 ) may be obtained. In another design condition, it is obvious that the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may be obtained simultaneously according to another equation. For example, in  FIG. 5 , when the sum of the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  is equal to the entire width A of the positive electrode plate  110  and the negative electrode plate  120 , Equation 6 is obtained. 
         [0000]        w   1   +w   2   =A   (6)
 
         [0048]    In this case, by combining Equations 5 and 6, the maximum and minimum values of the positive electrode boundary interval w 1  and the negative electrode boundary interval w 2  may be obtained. 
         [0049]    Referring to  FIG. 6 , a modified example of the positive electrode plate  110  of  FIG. 2  will now be described. Referring to  FIGS. 2 ,  4 A,  4 B, and  5 , the positive active material  112  covers the positive electrode material  111 , and the positive electrode non-coated portion  111   a  with a width w 1  that is smaller than an entire width A of the positive electrode material  111  extends from the positive electrode material  111 . However, since the heat amount Q 1  per unit area of the positive electrode plate  110  is 
         [0000]    
       
         
           
             
               
                 
                   ( 
                   
                     C 
                     
                       
                         w 
                         1 
                       
                        
                       
                         d 
                         1 
                       
                     
                   
                   ) 
                 
                 2 
               
                
               
                 R 
                 1 
               
                
               t 
             
             , 
           
         
       
     
         [0000]    as the positive electrode boundary interval w 1  is increased, the heat amount Q 1  per unit area of the positive electrode plate  110  is reduced. Thus, in  FIG. 6 , in order to increase a positive electrode boundary interval w 3  in a positive electrode plate  1110 , the positive electrode boundary interval w 3  may be equal to a width of a positive electrode material  1111 . In this case, positive electrode non-coated portions  1111   a  and  1111   b  may include a first positive electrode non-coated portion  1111   b  extending from the positive material  1111  so as to have the same width as that of the positive material  1111 , and a second positive electrode non-coated portion  1111   a  extending from the positive material  1111  so as to have a smaller width than that of the positive material  1111 . In this case, the negative electrode non-coated portion  121   a  has the same structure as in  FIG. 2 . That is, the electrode assembly  100  may include the positive electrode plate  1110  of  FIG. 6 , the negative electrode plate  120  of  FIG. 2 , and the separator  130  interposed therebetween. 
         [0050]    Thus, the first positive electrode non-coated portion  1111   b  of  FIG. 6  is the same or similar as the width of the negative electrode non-coated portion  121   a  of  FIG. 2 , and the positive electrode boundary interval w 3  of  FIG. 6  may be greater than the negative electrode boundary interval w 2  of  FIG. 4B . 
         [0051]    It should be understood that the exemplary embodiments described therein 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. Thus, the scope of the pending application should not be limited to the foregoing description, but should be defined by the appended claims.