Abstract:
A secondary battery is disclosed. In one aspect, the battery includes an electrode assembly including i) a positive electrode plate on which a positive active material is formed, ii) a negative electrode plate on which a negative active material is formed, and iii) a separator separating the positive and negative electrode plates. The battery also includes a can accommodating the electrode assembly, wherein the can has an inner surface facing the electrode assembly, an inner active material layer formed on the inner surface of the can and a securing layer covering the inner active material layer.

Description:
RELATED APPLICATION 
     This application claims priority to and the benefit of Provisional Patent Application No. 61/810,660 filed on Apr. 10, 2013 in the U.S Patent and Trademark Office, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The described technology generally relates to secondary batteries. 
     2. The Description of the Related Technology 
     In general, a secondary (rechargeable) battery includes i) an electrode assembly in a cylindrical shape, ii) a can coupled to the electrode assembly, iii) an electrolyte injected into the inside of the can to allow lithium ions to move, and iv) a cap assembly coupled to one side of the can, preventing a leakage of the electrolyte, and preventing a removal of the electrode assembly. Such a secondary battery usually has a capacity from about 2000 mA to about 4000 mA, and thus the secondary battery is mainly mounted in portable devices such as a notebook computer, a digital camera, and a camcorder that generally require a large capacity of power. As an example, multiple secondary batteries are connected to one another in series or in parallel, assembled as a hard pack having a predetermined shape in which a protection circuit is mounted, coupled to an electronic device, and used as a power supply. 
     A method of manufacturing the secondary battery stacks a negative plate coated with a negative active material, a separator, and a positive plate coated with a positive active material, couples one end of the stack structure to a winding axis having a pole shape, approximately rolls the stack structure in a cylindrical shape, and forms the electrode assembly. Thereafter, the electrode assembly is inserted into the cylindrical can. Then, the electrolyte is injected into the cylindrical can, and the cap assembly is coupled to a top portion of the cylindrical can, and thus a lithium ion battery having a cylindrical shape is completed. 
     SUMMARY 
     One inventive aspect is a secondary assembly having improved charging and discharging capacity. 
     Another aspect is a secondary battery which includes an electrode assembly formed by stacking and winding a positive electrode plate in which a positive active material is disposed, a negative electrode plate in which a negative active material is disposed, and a separator, a can accommodating the electrode assembly, an inner active material layer formed by disposing one of the positive active material and the negative active material in an inner surface of the can, and a ceramic layer formed to cover the inner active material layer. 
     The can may have a cylindrical or angular shape. A cross-section of the inner active material layer may have a wave shape. A groove may be formed in the inner active material layer. The ceramic layer may include at least one of a metal oxide, a metal nitride, a metal hydroxide, and a metal phosphide. 
     The metal oxide may be an oxide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. The metal nitride may be a nitride of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. The metal hydroxide may be a hydroxide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. The metal phosphide may be a phosphide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. 
     Another aspect is a secondary battery, comprising: an electrode assembly comprising i) a positive electrode plate on which a positive active material is formed, ii) a negative electrode plate on which a negative active material is formed, and iii) a separator separating the positive and negative electrode plates; a can accommodating the electrode assembly, wherein the can has an inner surface facing the electrode assembly; an inner active material layer formed on the inner surface of the can; and a securing layer covering the inner active material layer. 
     In the above battery, the securing layer is formed of a material comprising ceramic. In the above battery, the inner active material layer is formed of a material substantially similar to one of the positive and negative active materials. In the above battery, the inner active material layer has a substantially uniform thickness. In the above battery, the thickness of the securing layer is in the range from about 2 μm to about 6 μm. In the above battery, the surface of the inner active material layer is non-planar. In the above battery, the surface of the inner active material layer has a wave shape. 
     In the above battery, the inner active material layer is discontinuous. In the above battery, the securing layer is formed of a material comprising at least one of a metal oxide, a metal nitride, a metal hydroxide, and a metal phosphide. In the above battery, each of the metal oxide, the metal nitride, the metal hydroxide and the metal phosphide comprises at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. In the above battery, the separator is formed on the outermost surface of the electrode assembly. 
     In the above battery, the securing layer is formed of a material comprising heat resistant resin. In the above battery, the heat resistant resin comprises at least one of the following: aramid resin, polyamideimide resin and polyimide resin. In the above battery, the ratio of the heat resistant resin and the remaining component of the securing layer is in the range from about 50 wt %:about 50 wt. % to about 90 wt. %:about 10 wt. %. In the above battery, the ratio of the heat resistant resin and the remaining component of the layer is in the range from about 60 wt %:about 40 wt. % to about 80 wt. %:about 20 wt. %. 
     Another aspect is a secondary battery, comprising: an electrode assembly having a first portion which is coated with a positive active material and a second portion which is coated with a negative active material, and wherein the first portion is separated from the second portion; a can accommodating the electrode assembly, wherein the can has an inner surface facing the electrode assembly, and wherein the inner surface is coated with one of the positive and negative active materials; and a securing layer at least partially covering the coated inner surface of the can. 
     In the above battery, the securing layer has a surface contacting the inner surface of the can, and wherein a plurality of concave portions and a plurality of convex portions are alternately formed on the surface of the securing layer. 
     Another aspect is a secondary battery, comprising: a can accommodating an electrode assembly, wherein the can has an inner surface facing the electrode assembly, and wherein the can has an electrical polarity; an inner active material layer formed on the inner surface of the can, wherein the inner active material layer is formed of an active material having the same electrical polarity as the can; and a ceramic layer at least partially covering the inner active material layer. 
     In the above battery, the ceramic layer has a surface contacting the inner surface of the can, and wherein a plurality of concave portions and a plurality of convex portions are alternately formed on the surface of the ceramic layer. In the above battery, the inner active material layer is discontinuous. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a secondary battery, according to an embodiment. 
         FIG. 2  is a schematic cross-sectional view taken from a line II-II′ of  FIG. 1 . 
         FIG. 3A  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are formed in an inner surface of a can, according to an embodiment. 
         FIG. 3B  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are formed in an inner surface of a can, according to another embodiment. 
         FIG. 4  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are foamed in an inner surface of a can, according to another embodiment. 
         FIG. 5  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are formed in an inner surface of a can, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be described with reference to the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In the drawings, the thicknesses of layers and regions may be exaggerated for clarity. 
       FIG. 1  is a schematic perspective view of a secondary battery  100 , according to an embodiment.  FIG. 2  is a schematic cross-sectional view taken from a line II-II′ of  FIG. 1 .  FIG. 3A  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are formed in an inner surface of a can, according to an embodiment.  FIG. 3B  is a partial cross-sectional view of an inner active material layer and a ceramic layer that are formed in an inner surface of a can, according to another embodiment. 
     As shown in  FIGS. 1 through 3 , the secondary battery  100  may include an electrode assembly  110 , a can  120 , and a cap assembly  130 . 
     In some embodiments, the electrode assembly  100  is formed by sequentially stacking and winding a negative electrode plate  111 , a separator  112 , and a positive electrode plate  113  in a jelly-roll shape. The negative electrode plate  111  may be formed of a copper (Cu) foil and is coated with a negative active material such as graphite. 
     The separator  112  is disposed between the negative and positive electrode plates  111  and  113 , functions to prevent a short and move lithium ions only, and may be formed of a material such as polyethylene (PE), polypropylene (PP), etc. The positive electrode plate  113  may be formed of an aluminum (Al) foil and is coated with a positive active material such as lithium cobalt oxide (LiCoO 2 ). A positive electrode tap  114  protruding upward from the positive electrode plate  113  may be installed in the center of the electrode assembly  110 . The positive electrode tap  114  may be formed of aluminum (Al). 
     A negative electrode tap  115  protruding downward from the negative electrode plate  111  may be installed in the center of the electrode assembly  110 . The negative electrode tap  115  may be formed of nickel (Ni), and is electrically connected to one surface of the can  120 . 
     The negative electrode plate  111 , the negative active material, the separator  112 , the positive electrode plate  113 , the positive electrode tap  114 , and the negative electrode tap  115  are not limited to the above-described materials and other materials may be used. 
     The can  120  accommodates the electrode assembly  110  and may have an exterior in a cylindrical shape. The can  120  may be formed of steel, stainless steel, aluminum, or an equivalent thereof, and other materials. Although the exterior of the can  120  according to the present embodiment has the cylindrical shape, the present invention is not limited thereto. That is, the exterior of the can  120  may have an angular shape. 
     A beading part  121  sunken inward is formed in a side surface of the can  120 . The beading part  121  firmly fixes and supports the cap assembly  130  to the can  120  to prevent the cap assembly  130  from being separated and to prevent an electrolyte from leaking to the outside. Meanwhile, an inner active material layer  122  is formed in an inner surface  120   a  of the can  120 . 
     The inner active material layer  122  may be formed by disposing a negative active material that is the same as or different from that coated on the negative electrode plate  111  in the inner surface  120   a  of the can  120 . In this case, the can  120  is used as a negative electrode basic material and thus a filling amount of the negative active material may be increased by an area of the inner surface  120   a  of the can  120 . Further, in this case, a part of the electrode assembly  110  that is the closest to the inner surface  120   a  of the can  120  is configured as the positive electrode plate  113  in which the positive active material is disposed so that charging and discharging responses may occur. 
     In some embodiments, the inner active material layer  122  has a substantially uniform thickness along the inner surface  120   a  of the can  120  as shown in  FIG. 3A . Although the inner active material layer  122  according to the present embodiment has the uniform thickness along the inner surface  120   a  of the can  120 , the present invention is not limited thereto. For example, as shown in  FIG. 4 , an inner active material layer  222  may be formed in a wave shape along the inner surface  120   a  of the can  120 . That is,  FIG. 4  is a partial cross-sectional view of the inner active material layer  222  and a ceramic layer  223  formed in the inner surface  120   a  of the can  120 , according to another embodiment. A cross-sectional view of the inner active material layer  222  formed in the inner surface  120   a  of the can  120  has the wave shape in which a concave portion  222   a  concaved toward the inner active material layer  222  and a convex portion  222   b  protruding from the inner active material layer  222  are alternatively repeated. This structure increases a contact area between the ceramic layer  223  disposed to cover the inner active material layer  222  and the inner active material layer  222 , thereby further enhancing a function of preventing the inner active material layer  222  from being separated and a function of the ceramic layer  223  relating to a battery stability. 
       FIG. 5  is a partial cross-sectional view of the inner active material layer  322  and a ceramic layer  323  formed in the inner surface  120   a  of the can  120 , according to another embodiment. As shown in  FIG. 5 , an inner active material layer  322  may have a substantially uniform thickness along the inner surface  120   a  of the can  120 , and concurrently predetermined grooves  322   a  may be formed in the inner active material layer  322 . In some embodiments, the grooves  322   a  are formed in the inner active material layer  322  formed in the inner surface  120   a  of the can  120 . This structure increases a contact area between the ceramic layer  323  disposed to cover the inner active material layer  322  and the inner active material layer  322 , thereby further enhancing a function of preventing the inner active material layer  322  from being separated and a function of the ceramic layer  323  relating to a battery stability. 
     Although the inner active material layer  122  formed in the inner surface  120   a  of the can  120  is formed of the negative active material in the present embodiment, the present invention is not limited thereto. For example, the inner active material layer  122  formed in the inner surface  120   a  of the can  120  may be formed of the positive active material. In this case, a part of the electrode assembly  110  that is the closest to the inner surface  120   a  of the can  120  is configured as the negative electrode plate  111  in which the negative active material is disposed so that charging and discharging responses may occur. A ceramic layer (or securing layer)  123  may be formed in the inner surface  120   a  of the can  120  to cover the inner active material layer  122 . 
     In one embodiment, as shown in  FIG. 3A , the ceramic layer  123  is continuously formed on the inner surface  120   a  of the can  120 . In another embodiment, as shown in  FIG. 3B , the ceramic layer  123  is discontinuously formed on the inner surface  120   a  of the can  120 . 
     The ceramic layer  123  may be formed of at least one of a metal oxide, a metal nitride, a metal hydroxide, and a metal phosphide. The ceramic layer  123  performs a function of preventing the inner active material layer  122  from being separated. That is, the ceramic layer  123  is formed to be firmly adhered to the inner active material layer  122  so that the inner active material layer  122  is prevented from being separated from the inner surface  120   a  of the can  120  although a shock is applied to an external surface of the secondary battery  100 . Further, the ceramic layer  123  increases a stability of the secondary battery  100 , and, in particular, may reduce a danger of heating and explosion due to overcharging. 
     The metal oxide may be an oxide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. For example, the metal oxide may be Al 2 O 3 , MgO, TiO 2 , Cr 2 O 3 , ZrO 2 , CaO, or SiO 2 . The metal nitride may be a nitride of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. The metal phosphide may be a phosphide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. The metal hydroxide may be a hydroxide of metal including at least one of Al, Ti, Cr, Zr, Ca, Si, and Mg. For example, the metal hydroxide may be Al(OH) 2 , Mg(OH) 2 , or Ti(OH) 4 . 
     Meanwhile, the thickness of the ceramic layer  123  may be from about 2 μm to about 6 μm in consideration of a mobility of lithium ions. The present invention is not limited thereto. The ceramic layer  123  may have different thicknesses. 
     The ceramic layer  123  may further include heat resistant resin as a binder. The heat resistant resin may use aramid resin, polyamideimide resin, polyimide resin. A ratio of the heat resistant resin in the ceramic layer  123  may be from about 50 wt %:50 wt % to about 90 wt %:about 10 wt % or may be from about 60 wt %:about 40 wt % to about 80 wt %:about 10 wt %. 
     Meanwhile, although the ceramic layer  123  according to the present embodiment is away from the separator  112  disposed in the outermost part of the electrode assembly  110 , the present invention is not limited thereto. That is, according to the present embodiment, the ceramic layer  123  may be disposed to contact the separator  112  disposed in the outermost part of the electrode assembly  110 . Meanwhile, the cap assembly  130  includes a fixed plate  131 , an insulator  132 , a variable plate  133 , a cap cover  134 , and a gasket  135 . 
     The fixed plate  131  is electrically connected to the positive electrode tap  114 . A vent hole  131   a  is formed in the fixed plate  131 . The insulator  132  is stacked on an upper surface of the fixed plate  131  and is formed of an electrically insulating material. 
     The variable plate  133  is coupled to an upper opening of the can  120  and electrically connected to the fixed plate  131 . The variable plate  133  may be formed in a structure and of a material that may be modified due to a battery inner pressure. The cap cover  134  is installed in an upper portion of the variable plate  133 . A plurality of through holes  134   a  are formed in the cap cover  134  so as to easily discharge gas. 
     The gasket  135  is formed of an approximately ring shape and has a function of insulating the fixed plate  131 , the insulator  132 , the variable plate  133 , and the cap cover  134  from the inner surface  120   a  of the can  120 . Meanwhile, an electrolyte (not shown) is injected into the inside of the can  120  and functions to move lithium ions generated by an electrochemical response in the negative electrode plate  111  and the positive electrode plate  113  of a battery during charging and discharging. 
     The electrolyte may be a non-water based organic electrolyte that is a mixture of lithium salt and a high purity organic solvent. Also, although the electrolyte may be a polymer using a polymer electrolyte, it will be understood that the type of electrolyte can be modified in various ways. 
     As described above, the inner active material layer  122  is formed in the inner surface  120   a  of the can  120 , which increases the filling amount of an active material according to the area of the inner surface  120   a  of the can  120 , thereby enhancing the performance of the secondary battery  100 . The ceramic layer  123  is formed to cover the inner active material layer  122 , which prevents the inner active material layer  122  from peeling off and provides enhanced stability during overcharging. 
     At least one of the disclosed embodiments improves charging and discharging capacity, prevents a removal of an inner active material layer, and improves overcharging stability. 
     It should be understood that the above embodiments 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.