Abstract:
Disclosed herein is a battery cell including an electrode assembly of a cathode/separator/anode structure, the electrode assembly being impregnated with electrolyte, the electrode assembly being chargeable and dischargeable, a battery case in which the electrode assembly is mounted, the battery case being made of aluminum or an aluminum alloy, and a protective coating layer applied to at least a portion of an outer surface of the battery case, the protective coating layer containing an electrically insulative polymer material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/KR2013/000822 filed on Feb. 1, 2013, which claims priority under 35 U.S.C. §119(a) to Patent Application No. 10-2012-0012100 filed in the Republic of Korea on Feb. 7, 2012, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an embedded type battery cell, and, more particularly, to a battery cell including an electrode assembly of a cathode/separator/anode structure, the electrode assembly being impregnated with an electrolyte, the electrode assembly being chargeable and dischargeable, a battery case in which the electrode assembly is mounted, the battery case being made of aluminum or an aluminum alloy, and a protective coating layer applied to at least a portion of an outer surface of the battery case, the protective coating layer containing an electrically insulative polymer material. 
     BACKGROUND ART 
     As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries as an energy source has also sharply increased. 
     Depending upon kinds of external devices in which secondary batteries are used, the secondary batteries may be used in the form of a single battery or in the form of a battery pack having a plurality of unit cells electrically connected to one another. For example, small-sized devices, such as mobile phones, can be operated for a predetermined period of time with the power and the capacity of one battery. On the other hand, a battery pack including a plurality of batteries needs to be used in middle or large-sized devices, such as laptop computers, portable digital versatile disc (DVD) players, small-sized personal computers (PCs), electric vehicles, and hybrid electric vehicles, because high power and large capacity are necessary for the middle or large-sized devices. 
     Among secondary batteries, a lithium secondary battery is widely used since the lithium secondary battery has high power and large capacity. 
     However, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary batter may be heated or explode due to overcharge of the lithium secondary battery, overcurrent in the lithium secondary battery, or other external physical impact applied to the lithium secondary battery. That is, the safety of the lithium secondary battery is very low. 
     Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as overcharge of the lithium secondary battery or overcurrent in the lithium secondary battery, are loaded on a battery cell in a state in which the safety elements are connected to the battery cell. 
     Generally, the PCM is electrically connected to the battery cell via conductive nickel plates by welding or soldering. That is, nickel plates are connected to electrode tabs of the PCB by welding or soldering, and the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack. 
     It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. To this end, a plurality of parts is necessary, which complicates an assembly process of the battery pack. In addition, a space necessary to receive the battery cell is reduced. 
     Furthermore, a battery case to receive the parts is made of conductive metal exhibiting high electric conductivity, such as metal plated with aluminum, an aluminum alloy, or nickel. As a result, a short circuit may be caused in the battery cell when the battery case contact other parts of the battery cell. 
     Consequently, there is a high necessity for a battery cell that is capable of securing a receiving space and insulativity of the battery cell and, at the same time, preventing the outer surface of a battery case from being corroded or worn while using a conventional battery cell and a conventional assembly method. 
     DISCLOSURE 
     Technical Problem 
     Therefore, the present invention has been made to solve the above problems and other technical problems that have yet to be resolved. 
     As a result of a variety of extensive and intensive studies and experiments to solve the problems as described above, the inventors of the present application have developed a battery cell wherein a battery case is coated with a polymer material to improve insulativity and capacity of the battery cell and completed the present invention. 
     Therefore, it is an object of the present invention to provide a battery cell wherein the outer surface of an aluminum battery case is coated with an electrically insulative polymer material to improve corrosion resistance, wear resistance, and insulativity of the battery case. 
     Technical Solution 
     In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a battery cell including an electrode assembly of a cathode/separator/anode structure, the electrode assembly being impregnated with an electrolyte, the electrode assembly being chargeable and dischargeable, a battery case in which the electrode assembly is mounted, the battery case being made of aluminum or an aluminum alloy, and a protective coating layer applied to at least a portion of an outer surface of the battery case, the protective coating layer containing an electrically insulative polymer material. 
     In the battery cell according to the present invention, therefore, durability and corrosion resistance of the battery case are greatly improved by the provision of the protective coating layer containing the electrically insulative polymer material. Also, it is not necessary to use an additional member, such as a label, thereby improving manufacturing efficiency of the battery cell and providing capacity greater than that of other battery cells having the same standard. 
     The protective coating layer may be variously formed using various copolymer components. 
     In a first example, the protective coating layer may be formed by applying an acryl resin as a primer and a urethane resin as a coating base material to the battery case and drying the acryl resin and the urethane resin. 
     In a second example, the protective coating layer may be formed by applying an epoxy resin as a primer and an acryl resin as a coating base material to the battery case and drying the epoxy resin and the acryl resin. 
     In a third example, the protective coating layer may be formed by applying a mixed solution of an acryl resin and a silicon resin to the battery ease and hardening the mixed solution using a hardening agent. 
     However, the material for the protective coating layer and the method of forming the protective coating layer are not limited thereto. 
     The battery case may have various forms. For example, the battery case may be a prismatic metal container; however, the battery case is not limited thereto. 
     In a preferred example, the protective coating layer may be applied to the outer surface of the battery ease in a state in which an uncoated margin section having a predetermined length is provided downward from an outer circumference of an upper end of the battery case. The uncoated margin section provides easily weldability, for example, when laser welding is carried out after a cap plate is mounted to an open upper end of the battery case. 
     More preferably, the uncoated margin section extends downward from the outer circumference of the upper end of the battery case by a length of 0.5 to 5 mm. If the length of the uncoated margin section is too long, it may be difficult to achieve desired durability of the battery case based on the protective coating layer, which is not preferable. On the other hand, if the length of the uncoated margin section is too short, it may not be possible to easily carry out laser welding, which is not preferable. 
     The method of forming the uncoated margin section is not particularly restricted. For example, the uncoated margin section may be formed by coating the battery case in a state in which an insulation material is applied to the battery case or an insulator or an insulation tape is mounted or attached to the battery case and removing the insulation material, the insulator, or the insulation tape. 
     In a preferred example be protective coating layer may have a thickness of 0.01 to 0.05 mm. 
     Generally, the battery cell is activated during manufacturing of the battery cell. A battery cell activation process is a process of initially charging and discharging the battery cell in a state in which the electrode assembly is impregnated with an electrolyte to forming protective film on an anode surface. Two battery cell activation processes may be performed depending upon charge pin connection methods. Correspondingly, the construction of the battery cell according to the present invention may be modified. 
     The first battery cell activation process may be performed in a state in which a cathode charge pin and an anode charge pin are connected to an upper end of the battery cell, and the protective coating layer may be applied throughout a bottom of the battery case. 
     The second battery cell activation process may be performed in a state in which an anode (or cathode) charge pin is connected to an upper end of the battery cell and a cathode (or anode) charge pita is connected to a lower end of the battery cell, and the protective coating layer may be applied to a bottom of the battery case excluding a connection opening section, to which the cathode (or anode) charge pin is connected. 
     The shape of the connection opening section is not particularly restricted so long as the connection opening section corresponds to the charge pins. For example, the connection opening section may be formed in a circular, oval, or polygonal shape in plan. 
     The connection opening section may be formed by coating the battery case in a state in which an insulation material is applied to a portion of the bottom of the battery case or an insulator or an insulation tape is mounted or attached to a portion of the bottom of the battery case and removing the insulation material, the insulator, or the insulation tape. 
     In another preferred example, the battery case may be a cylindrical battery case. 
     The protective coating layer may be applied throughout a side of the cylindrical battery case. 
     A battery cell activation process, which is carried out during manufacturing of the battery cell, may be performed in a state in which a cathode (or anode) charge pin is connected to an upper end of the battery cell and an anode (or cathode) charge pin is connected to a lower end of the battery cell, and the protective coating layer may be applied to a bottom of the battery case excluding a connection opening section, to which the anode (or cathode) charge pin is connected. 
     Specifically, the connection opening section may be formed by coating the battery case in a state in which an insulation material is applied to a portion of the bottom of the battery case or an insulator or an insulation tape is mounted or attached to a portion of the bottom of the battery case and removing the insulation material, the insulator, or the insulation tape. 
     In the above-mentioned examples, the connection opening section may be sealed using an insulation member after the battery cell activation process. 
     The material for the insulation member is not particularly restricted so long as the insulation member protects the connection opening section from the outside and maintains electrical insulation of the connection opening section. 
     The kind of the battery cell is not particularly restricted. For example, the battery cell may be a lithium secondary battery cell. The secondary battery may be a single battery including one battery cell or an assembled battery including two or more battery cells. Therefore, the secondary battery is not denoted by a specific title. 
     The composition, structure, and manufacturing method of the secondary battery, including the lithium secondary battery, is obvious to a person having an ordinary skill in the part to which the present invention pertains, and therefore, a detailed description thereof will be omitted. 
     In accordance with another aspect of the present invention, there is provided a secondary battery pack including the battery cell with the above-stated construction mounted in a pack case. The secondary battery pack may be an embedded pack. 
     In accordance with a further aspect of the present invention, there is provided a mobile device including the secondary battery pack with the above-stated construction embedded therein as a power source. Specifically, the mobile device may be a thin laptop computer, a tablet PC, or a smart pad; however, the mobile device is not limited thereto. 
     Also, the secondary battery pack may be used as a power source for an electric vehicle (EV), a hybrid electric vehicle (REV), a plug-in hybrid electric vehicle (PHEV), or a power storage device. 
     The above device or apparatuses are well known in the part to which the present invention pertains, and therefore, a detailed description thereof will be omitted. 
     Effects of the Invention 
     As is apparent from the above description, a protective coating layer containing an electrically insulative polymer material is formed at the entire surface of the battery case in a state in which a connection opening section is provided at a specific region of the battery case as needed, thereby improving corrosion resistance, wear resistance, and insulativity of the battery case. 
     Also, an additional process of attaching a label to the outer surface of the battery case is not necessary, thereby easily manufacturing the battery cell and providing capacity greater than that of other battery cells having the same standard. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view showing a battery pack according to an embodiment of the present invention; 
         FIG. 2  is a typical view showing a method of forming a protective coating layer at a battery cell according to an embodiment of the present invention; 
         FIG. 3  is a partial perspective view showing the upper end of the battery cell according to the embodiment of the present invention; 
         FIG. 4  is a partial side view of  FIG. 3 ; 
         FIG. 5  is a front view showing the battery cell to which connection pins, which are used during a charging process to activate the battery cell, are coupled; 
         FIG. 6  is an exploded perspective view showing the battery cell, a protective coating layer, and an insulation tape; 
         FIG. 7  is a partial perspective view showing the lower end of the battery cell; 
         FIG. 8  is an exploded perspective view showing a cylindrical battery cell according to another embodiment of the present invention and a protective coating layer; and 
         FIG. 9  is a bottom view showing the bottom of the cylindrical battery cell according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted, however, that the scope of the present invention is not limited by the illustrated embodiments. 
       FIG. 1  is an exploded perspective view showing a battery pack according to an embodiment of the present invention, and  FIG. 2  is a typical view showing a method of forming a protective coating layer at a battery cell according to an embodiment of the present invention. 
     Referring to these drawings, a secondary battery pack  100  according to the present indention includes a battery cell  110 , an insulative mounting member  220 , a protection circuit board  230 , a pair of connection members  210  and  212 , a top cap  240 , and a battery case  150  having a protective coating layer  155  applied thereto. The insulative mounting member  220 , the connection members  210  and  212 , the protection circuit board  230 , and the top cap  240  are sequentially mounted to the top of the battery cell  110 . 
     The insulative mounting member  220  is provided with openings (not shown), through which electrode terminals  253  and  254  of the battery cell  110  are exposed. The insulative mounting member  220  is directly loaded on the top of the battery cell  110 . The insulative mounting member  220  may be coupled to the top of the battery cell  110  using a bonding agent. 
     The insulative top cap  240  is coupled to the upper end of the battery cell  110  while surrounding the insulative mounting member  220  in a state in which the connection members  210  and  212  and the protection circuit board  230  are loaded on the insulative top cap  240 . Also, the insulative top cap  240  extends downward by a predetermined length to surround the outer circumference of the upper end of the battery cell  110 . 
     The protective coating layer  155  may be formed by spraying a coating solution containing an insulative polymer material on the outer surface of the battery cell  110  using sprayers  250  and drying the coating solution, for example, as shown in  FIG. 2 . 
       FIG. 3  is a partial perspective view showing the upper end of the battery cell,  FIG. 4  is a partially enlarged side view of  FIG. 3 ,  FIG. 5  is a front view showing the batter cell to which connection pins, which are used during a charging process to activate the battery cell, are coupled,  FIG. 6  is an exploded perspective view showing the battery cell, a protective coating layer, and an insulation tape, and  FIG. 7  is a partial perspective view showing the lower end of the battery cell. 
     Referring to these drawings, a protective coating layer  155  (see  FIG. 2 ) is formed at the entire surface of the battery case  150  in a state in which an uncoated margin section  151  having a length h of about 3 mm is provided downward from the outer circumference of the upper end of the battery case  150 . The uncoated margin section  151  is formed by coating the battery case  150  in a state in which an insulation material (not shown) is temporarily applied to the battery case  150  and removing the insulation material. 
     Also, the battery cell  110  having an electrode assembly of a cathode/separator/anode structure disposed in the battery case  150  made of aluminum together with an electrolyte in a sealed state is manufactured as follows. First, a protective coating layer  155  is formed at the entire surface of the battery case  150  in a state in which a connection opening section  162 , to which charge pins  160  and  161  used to activate the battery cell  110  are connected, is formed at the bottom  159  of the batter case  150 . Subsequently, the electrode assembly is mounted in the battery case  150 , laser welding is carried out at the open upper end of the battery case  150  along the outer circumference of the battery cell  110  above a cap plate  152  (see an arrow shown in  FIG. 3 ), an electrolyte is injected through an electrolyte injection port  153  of the cap plate  152 , and the battery cell is activated. Subsequently, the electrolyte is replenished, and then the electrolyte injection port  153  is sealed. 
     The connection opening section  162  is formed in a quadrangular shape in plan. Alternatively, the connection opening section  162  may be formed in various shapes in plan. 
     The connection opening section  162  is formed by forming the protective coating layer  155  at the battery case  150  in a state in which an insulation material (not shown) is applied to a portion of the bottom of the battery case  150  and removing the insulation material. 
     Finally, the connection opening section  162  is sealed using an insulation member  165 , such as an insulation tape. 
     The battery cell activation process is performed in a state in which the first charge pin  160  is connected to an upper electrode terminal  131  of the cap plate  152  and the second charge pin  161  is connected to the connection opening section  162  of the battery case  150 . 
     Consequently, the connection of the second charge pin  161  is easily achieved by the provision of the connection opening section  162 . 
       FIG. 8  is an exploded perspective view showing a cylindrical battery cell according to another embodiment of the present invention and a protective coating layer, and  FIG. 9  is a bottom view showing the bottom of the cylindrical battery cell according to the embodiment of the present invention. 
     Referring to these drawings, a cylindrical battery cell  300  has an electrode assembly disposed in a cylindrical battery case  350  together with an electrolyte in a sealed state. A protective coating layer  500  is formed at the entire surface of the battery case  350  excluding a connection opening section  360 , to which charge pins (not shown) used to activate the battery cell  300  are connected. 
     A cathode terminal  320  is formed at the top  310  of the cylindrical battery cell  300  such that the cathode terminal  320  protrudes upward in a state in cathode terminal  320  is isolated from the battery case  350 . An anode terminal  330  is formed at the bottom of the battery cell  300 . 
     A method of forming the protective coating layer  500  at the entire surface of the battery case  350  excluding the connection opening section  360  of the cylindrical battery cell  300  is identical to what has been described above with reference to  FIGS. 1 to 7  except that the uncoated margin section  151  (see  FIG. 4 ) is formed, and therefore, a description thereof will be omitted. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.