Patent Publication Number: US-2007094865-A1

Title: Packaged thin film batteries and methods of packaging thin film batteries

Description:
REFERENCE TO RELATED APPLICATION  
      This is a continuation-in-part of U.S. patent application Ser. No. 10/047,407 filed Jan. 10, 2002. 
    
    
     TECHNICAL FIELD  
      This invention relates generally to thin film batteries, and more particularly to packaged thin film batteries and methods of packaging thin film batteries.  
     BACKGROUND OF THE INVENTION  
      The metal lithium of thin film batteries reacts rapidly upon exposure to atmospheric elements such as oxygen, nitrogen, carbon dioxide and water vapor. Thus, the lithium anode of a thin film battery will react in an undesirable manner upon exposure to such elements if the anode is not suitably protected. Other components of a thin film battery, such as a lithium electrolyte and cathode films, also require protection from exposure to air, although these components are commonly not as reactive as thin metal anode films. It should therefore be desirable to incorporate within a lithium or lithium intercalation compound battery, which includes an anode of lithium and other air-reactive components, a packaging system that satisfactorily protects the battery components from exposure to air.  
      Polymer batteries have been constructed in a-manner in which the battery has a porous anode and cathode. The partially constructed battery cell is then placed within a protective “bag” which is sealed along three edges. Once the battery cell is positioned within the bag a liquid electrolyte is injected into the bag to occupy the space within the porous spacer between the anode and cathode. The open edge or forth edge of the bag is then heat sealed, as shown in U.S. Pat. No. 6,187,472. During the last steps of this process however air or other gases occupy spaces within the bag. These gases are entrapped within the bag once it is sealed. Much care must also be exercised during the sealing process to insure that the heat seal does not contact the battery cell within the bag as the heat will harm the polymer battery cell.  
      In the past packaging systems for batteries have been devised which included a shield which overlays the active components of the battery. These shields have been made of a ceramic material, a metallic material, and a combination of ceramic and metallic materials. The construction of thin film batteries however have proven to be quite difficult to produce and in providing an appropriate barrier as gas pockets may be capture between the anode and the protective layer during construction.  
      Another thin film battery packaging system has been devised wherein alternating layers of parylene and titanium are laid over the active components. The alternating layers are provided to restrict the continuation of pin holes formed in the layers during construction. This method of producing a protective layer has been difficult to achieve and has provided a protective layer which remains effective for only a short time.  
      It thus is seen that a need remains for a packaging system for thin film batteries which overcomes problems associated with those of the prior art. Accordingly, it is to the provision of such that the present invention is primarily directed.  
     SUMMARY OF THE INVENTION  
      In a preferred form of the invention, a method of sealing a battery cell having a top surface and peripheral edges, the method comprising the steps of positioning a packaging foil over the top surface of the battery cell, and heat sealing the packaging foil to the top surface of the battery cell. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional side-view of a thin film battery cell.  
       FIG. 2  is an illustration of the complete thin film battery having a protective packaging illustrating principles of the invention in a preferred embodiment, shown prior to passing through the laminator.  
       FIG. 3  is a partial cross-sectional side-view of the thin film battery cell and a pair of packaging foils and carriers shown subsequent to passing through a laminator.  
       FIG. 4  is a cross-sectional side-view of the thin film battery cell and a pair of packaging foils in another preferred form of the invention.  
       FIG. 5  is a cross-sectional side-view of the thin film battery cell and a pair of packaging foils in another preferred form of the invention.  
       FIG. 6  is a cross-sectional side-view of the thin film battery cell and a pair of packaging foils in another preferred form of the invention.  
       FIG. 7  is a cross-sectional side-view of the thin film battery cell and a pair of packaging foils in another preferred form of the invention. 
    
    
     DETAILED DESCRIPTION  
      With reference next to the drawings, there is shown in a packaged battery  10  embodying principles of the invention in a preferred form. The packaged battery  10  has a thin film lithium or lithium ion battery cell  11  encased within a packaging layer  12 . The battery cell  11  includes a substrate  13 , a cathode  14 , an electrolyte  15 , an anode  16 , a passivation layer  19 , a cathode anode current collector  18  and an anode current collector  17 . The cathode  14  is made of a lithium metal or lithium intercalation compound, preferably a metal oxide such as LiNiO 2 , V 2 O 5 , Li x Mn 2 O 4 , LiCoO 2  or TiS 2 . The electrolyte  15  is preferable made of lithium phosphorus oxynitride, Li x PO y N z . The anode  16  is preferably made of silicon-tin oxynitride, SiTON, when used in lithium ion batteries, or other suitable materials such as lithium metal, zinc nitride or tin nitride. Finally, an anode current collector  17  and cathode current collector  18  are preferably made of copper or nickel. The battery cell  11  is preferably manufactured in a manner described in detail in U.S. patent application Ser. No. 5,561,004, which is specifically incorporated herein.  
      With reference next to  FIG. 3 , to manufacture the battery  10  a bottom layer of packaging foil  21  is positioned to overlay the bottom surface of the substrate  13  while a top layer of packaging foil  22  is positioned to overlay the top surface of the passivation layer  19 . The bottom and top layers of packaging foils  21  and  22  may be a laminated sheet of Class PPD or Class ECR packaging material made by Shield Pack, Inc. These packaging foils have an inward facing layer of polymer P 1 , an outwardly facing layer of polymer P 2  and at least one intermediate layer of metal M, of course, the packaging foil may include several intermediate alternating layers of metal and polymer. A bottom sheet of carrier material  24  is positioned to overlay the bottom layer of packaging foil  21  while a top sheet of carrier material  25  is positioned to overlay the top layer of packaging foil  22 . The carrier materials  24  and  25  may be 5 mil thick sheets of Kapton made by Dupont.  
      The battery cell  11 , two layers of packaging foil  21  and  22 , and two layers of carrier material  24  and  25  are then passed through a laminator having a pair of heaters  28  and a pair of pressure applying means in the form of lamination rollers  29 . The packaging foils  21  and  22  become packaging layer  12  in the final product. The lamination rollers  29  are preferably made of a soft material such as rubber and are approximately  5  centimeter in diameter. The purpose of the carrier materials  24  and  25  is to provide an even pressure and temperature to the underlying packaging foil during the lamination process.  
      The temperature, pressure and rate of travel through the laminator causes the interior surface of the packaging foils  21  and  22  to be heat sealed to the corresponding surface of the battery cell  11  facing the packaging foils. As such, the interior surface of the bottom layer of packaging foil  21  is heat sealed to the bottom surface of the substrate  13  and the interior surface of the top layer of packaging foil  22  is heat sealed to the top surface of the passivation layer  19 , as shown in  FIG. 2 . Although within the scope of the present invention many different combinations of temperature, pressure and material travel speeds through the laminator may be discovered which heat seals the packaging layers to the battery cell. However, it has been discovered that a temperature of 155 degrees Celsius, a pressure of 5 p.s.i and a travel speed of 25 cm/min for a Class PPD packaging material produces a proper heat seal between the packaging foils and the battery cell.  
      It has been discovered that by heat sealing the packaging foils directly to the battery cell the battery cell is provided with a substantially improved protective layer thereby improving the overall packaged battery. This improvement is achieved in part by the lamination process wherein as the packaging foils are heat sealed to the battery cell and as such occurs the gases between the foils and the battery cell are driven out. The use of packaging materials with the prior art batteries produced spaces between the battery cell and the packaging material, thereby allowing the capture of gases within these spaces which could degrade the components of the battery cell. The process of laminating the packaging material directly to the battery cell also creates a smaller overall battery, a problem which exists wherein the space occupied by the battery is intended to be as small as possible. Lastly, the lamination process causes the packaging material to be bonded to the side edges of the battery cell, thereby once again eliminating space between the battery cell and packaging material wherein harmful gases may in entrapped. This is enhanced by the softness and diameter of the lamination rollers  29  which determine the extent to which the packaging foil is forced against, and thereby sealed within, the side edges and inward corners of the battery cell.  
      It should be understood that while the present invention strives to laminate the exterior surfaces of the battery cell completely with the packaging material, the invention is not limited to such. However, it is desirous to laminate at least a majority of the top surface of the battery cell, the active material surface, so as to be in sealing engagement with the packaging foil, thereby eliminating virtually all gases therebetween. The packaging foil may be one sheet of packaging foil folded over itself or two separate sheets of packaging foil. Also, the laminating process may be carried out with the use of a platen laminator which consists of pressure applying means in the form of two oppositely disposed heated plates which are moved towards each other in pressing the material therebetween. The lamination process is considered to be a heat sealing process wherein the combination of heat and pressure causes a bonding of the packaging foil to the underlying cell.  
      With reference next to  FIG. 4 , there is shown a battery cell  40  having a substrate  41  and active cells  42  on opposite sides of the substrate. Each active cell includes the typical cathode, electrolyte and anode. The cell also includes a cathode contact  44  and an anode contact  45 . The packaging foil  47  is positioned on opposite sides of the battery cell  40  and heat sealed to the top surface  48  of each active cell  42 . The packaging material is thereby bonded to a majority of the top surface  48 .  
      With reference next to  FIG. 5 , there is shown a battery cell  50  having a substrate  51  and active cells  52  on opposite sides of the substrate. Each active cell includes the typical cathode, electrolyte and anode. The cell also includes a cathode contact  54  and an anode contact  55 . The packaging foil  57  is positioned on opposite sides of the battery cell  50  and heat sealed to the top surface  58  of each active cell  52 . The packaging material is thereby bonded to a majority of the top surface  58 .  
      With reference next to  FIG. 6 , there is shown a battery cell  60  having a substrate  61  and an active cell  62 . The active cell  62  includes the typical cathode, electrolyte and anode. The cell also includes a cathode contact  64  and an anode contact  65 . The packaging foil  67  is positioned on the battery cell  60  and heat sealed to the top surface  68 . The packaging material is thereby bonded to a majority of the top surface  68 .  
      With reference next to  FIG. 7 , there is shown a battery cell  70  having a substrate  71  and an active cell  72 . The active cell  72  includes the typical cathode, electrolyte and anode. The cell also includes a cathode contact  74  and an anode contact  75 . The packaging foil  77  is positioned on the battery cell  70  and heat sealed to the top surface  78 . The packaging material is thereby bonded to a majority of the top surface  78 .  
      It should also be understood that the present invention is not limited to the use of lithium ion batteries and that the invention may be utilized with many types of thin film battery cells. Also, the arrangement of the cathode, electrolyte and anode may be inverted as compared to that shown in the drawings.  
      Lastly, it should be understood that the battery cell utilized in practicing the invention is not required to be passivated, as the packaging material can be heat sealed directly to the anode or anode current collector.  
      It thus is seen that a packaged battery is now provided which is sealed to prevent unwanted exposure to gases. It should of course be understood that many modifications may be made to the specific preferred embodiment described herein, in addition to those specifically recited herein, without departure from the spirit and scope of the invention as set forth in the following claims.