Abstract:
A flexible battery structure comprises a stack of a layer of cathode active material and anode active material separated by a layer of electrolyte and held between a cathode flexible substrate and an anode flexible substrate, wherein the cathode and anode substrates have a surface area larger than the surface area of the stacked layers to form and define overlapping end portions which are hermetically sealed with a water-resistant composite material. The outer surface of the cathode and outer surface of the anode form the positive polarity and negative polarity connection leads of the battery structure. The anode and cathode substrates are flexible to accommodate applications in which the battery is subjected to bending.

Description:
TECHNICAL FIELD 
     The present invention relates generally to battery structures and deals more particularly with a flexible battery structure. 
     BACKGROUND OF THE INVENTION 
     The advent of portable electronic devices such as laptop computers, mobile communication devices and personal digital assistants, for example, have created a demand for lightweight, high capacity batteries. Typical battery structures are somewhat rigid and typically are encased in a metallic can or other such rigid material to protect the battery and/or apply pressure to the battery components to create the necessary chemical reaction to produce electron flow. The use of such materials has limited the practical reduction in battery size and application of such batteries. Additionally, such battery materials could not accommodate applications wherein the battery structure encountered frequent flexing and bending such as in clothing apparel applications or wrist-worn products. 
     It was thought that lithium polymer batteries, which use a foil package made of a lamination of an aluminum layer between two plastic layers, would provide the desired flexibility for such applications. In reality, the aluminum is not able to withstand many bendings and thus does not provide the desired flexibility and reliability. In addition, the plastic lamination is susceptible to water impregnation, which reacts with the lithium to cause the battery to fail in a relatively short time. 
     A further disadvantage of such polymer batteries is the requirement that the electrode tabs must extend from within the plastic packaging to permit contact with an external electrical circuit with which the battery is used. It is difficult to completely seal the space through which the electrode tabs extend, which leads to an additional possible entry point for water impregnation. 
     Therefore, it is an object of the present invention to provide a flexible battery structure that can withstand repeated bending and flexing. 
     It is a further object of the present invention to provide a flexible battery structure that has a thinner profile thickness than equivalent conventional power density battery structures. 
     SUMMARY OF THE INVENTION 
     The present invention substantially obviates, if not entirely eliminates, the disadvantages of utilizing lithium polymer and other such batteries having foil packages made of a lamination of aluminum and plastic layers by providing a polymer battery wherein the outer packaging is eliminated entirely to reduce the thickness of the battery and allow flexing and bending of the battery structure. 
     In one aspect of the present invention, a flexible battery structure comprises a first flexible substrate having an inner surface face and an outer surface face defining a cathode; a layer of cathode active material adjacent to the inner surface face of the cathode substrate; a layer of electrolyte adjacent to the layer of cathode active material; a layer of anode active material adjacent to the electrolyte layer; a second flexible substrate having an inner surface and an outer surface face defining an anode wherein the anode inner surface is adjacent to the anode active material layer; and means for sealing the stack of layers formed between the first and second substrates. 
     Preferably, the cathode substrate and anode substrate have surface face areas larger than the stacked layers to define a marginal peripheral seam to sandwich the stacked layers. 
     Preferably, the marginal peripheral seam further comprises overlapping portions of each of the cathode substrate and anode substrate with respect to one another in a spaced relationship to prevent an electrical short circuit between said cathode substrate and said anode substrate. 
     Preferably, the marginal peripheral seam is hermetically sealed. 
     Preferably, the hermetic seal is comprised of a water-resistant composite material inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam. 
     Preferably, the cathode and anode substrates are made of a metal foil wherein the cathode substrate is copper and the anode substrate is aluminum. 
     Preferably, the cathode outer surface face and the anode outer surface face define the exterior surfaces of the battery structure. 
     Preferably, the cathode outer surface face comprises the positive polarity connection lead and the anode outer surface face comprises the negative polarity connection lead. 
     Preferably, the layer of electrolyte comprises means for separating the cathode substrate and the anode substrate. 
     In a further aspect of the invention, one or more glass balls are inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam to hermetically seal the seam between the cathode and anode substrates. Preferably, a non-electrically conductive, water-resistant composite material is inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam. 
     Other features and advantages of the present invention will become more apparent from an understanding of the following detailed description of presently preferred embodiments of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-section of a representative polymer battery. 
     FIG. 2 is a schematic cross-section of a flexible battery embodying the present invention. 
     FIG. 3 is a fragmentary top plan view of the flexible battery of FIG.  2 . 
     FIG. 4 is a schematic cross-section of an alternate embodiment of a flexible battery embodying the present invention. 
     FIG. 5 is a fragmentary top plan view of the flexible battery of FIG.  4 . 
     FIG. 6 is a schematic cross-section of another alternate embodiment of a flexible battery embodying the present invention. 
     FIG. 7 is a schematic cross-section of the flexible battery of FIG. 6 showing one possible connection arrangement with an external electrical circuit. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning to FIG. 1, a schematic cross-section of a representative polymer battery is illustrated therein and is generally designated  10 . The polymer battery  10  includes a typical construction comprising typical battery components, including a cathode  12 , cathode active material  14 , an electrolyte separator  16 , anode active material  18 , and an anode electrode  20 . The battery components are stacked using conventional production methods and the different battery component layers are held together by means of a foil package, generally designated  22 , comprising two lamination sheets  24 ,  26  in clam-shell-like arrangement to hold the battery component layers. Each lamination sheet  24 ,  26  is comprised of aluminum foil sandwiched by two plastic layers. The lamination sheets  24 ,  26  are held together by glue  28  or other adhesive means. A disadvantage of this construction is that the aluminum foil within the lamination  24 ,  26  does not withstand constant bending or flexing and eventually breaks, which allows moisture in the form of water to enter into the interior cavity  30 , and which moisture reacts with the cathode or anode active material leading to battery failure. A further disadvantage of this construction is that conventional glues and adhesives generally absorb moisture and allow water to enter into the interior cavity  30 . 
     Turning now to FIG.  2  and considering the present invention in further detail, a schematic cross-section of a flexible battery embodying the present invention is illustrated therein and generally designated  50 . The flexible battery  50  is comprised of a stack of layers starting with a first flexible substrate defining the cathode  52  having an outer surface  54  and inner surface  56 . A layer of cathode active material  58  is adjacent to the inner surface  56  of the cathode  52 . A layer of electrolyte  60  is adjacent to the cathode active material layer  58  to separate the cathode active material from the anode active material layer  62 . A second flexible substrate defining an anode  64  has an outer surface  66  and an inner surface  68  adjacent to the anode active material layer  62 . The cathode active material layer  58 , electrolyte  60  and anode active material layer  62  are contained on their respective edge ends by a retaining wall  70 ,  72 . The retaining walls  70 ,  72  are dimensioned to fit between the inner surface  56  of the cathode and the inner surface  68  of the anode  64  to contain the layers  58 ,  60 ,  62 . The cathode active material layer  58  may be a cobalt oxide, manganese oxide, nickel oxide or other material now known or future-developed and familiar to those skilled in the battery art. The anode active material layer  62  may be a graphite or other material now known or future-developed and familiar to those skilled in the battery art. 
     Preferably, the flexible substrate defining the cathode  52  is a thin, flexible copper substrate and the flexible substrate defining the anode  64  is a thin, flexible aluminum substrate. 
     An end portion, generally designated  74 , of the cathode substrate  52  extends beyond the retaining wall  72  and is oppositely disposed with an end portion, generally designated  76 , of the anode substrate  64 , which likewise extends beyond the end wall  72 . The overlapping end portions  74 ,  76  define a marginal peripheral seam, generally designated as  78 , and which marginal peripheral seam  78  extends completely around the peripheral edge of the battery  50 . In the illustrated embodiment shown in FIG. 2, the marginal peripheral seam  78  is filled with a water-resistant composite material  80  which functions to hold the cathode substrate  52  to the anode substrate  64  and to hermetically seal the marginal peripheral seam to make the battery structure watertight. The length L of the marginal peripheral seam needs to be sufficiently long to ensure that the water-resistant composite material  80  is of sufficient thickness to prevent water seepage or impregnation and also to provide a strong bonding surface between the cathode substrate  52  and anode substrate  64  to hold the battery structure together. The length of the marginal peripheral seam is measured from the retaining wall  72  to the ends  82 ,  84  of the cathode substrate  52 , anode substrate  64 , respectively. As illustrated in FIG. 2, the water-resistant composite material  80  extends beyond the ends  82 ,  84  to ensure that water cannot pass between the composite-to-substrate contact surface area. The surface  54  of the cathode  52  provides a positive polarity connection lead to an external circuit. The surface  66  of the anode  64  provides a negative polarity connection lead to an external electrical circuit. The absence of an outer foil package in the battery construction of the present invention provides a more durable construction for smaller radius bending and the ability to withstand frequent bendings without damage. 
     FIG. 3 is a fragmentary top plan view of the flexible battery structure illustrated in FIG. 2 as viewed looking down at the cathode surface  54 . FIG. 3 illustrates the marginal peripheral seam having a length L into which the water-resistant composite material  80  is inserted and which extends beyond the end  82  of the substrate defining the cathode  52 . Any suitable water-resistant composite material now known or future-developed that provides the desired sealing and holding property characteristics may be used. 
     Turning now to FIG. 4, a schematic cross-section of an alternate embodiment of a flexible battery structure embodying the present invention is illustrated therein and generally designated  100 . The flexible battery  100  is similar to the flexible battery  50  illustrated in FIG.  2  and includes a layer of cathode active material  102 , an electrolyte or separator layer  104 , anode active material layer  106 , sandwiched between the cathode  108  and anode  110 . The end portion  112  of the cathode and the end portion  114  of the anode are held in an oppositely disposed relationship to one another to define the marginal peripheral seam  116 . In the illustrated embodiment in FIG. 4, a plurality of glass balls or fiber balls  118  are inserted in the marginal peripheral seam  116  between the overlapping end portions  112 ,  114  of the cathode substrate  108  and of the anode substrate  110  respectively to create a hermetically sealed seam. The presence of the glass balls  118  allow the end portions  112 ,  114  to be squeezed together under pressure which forces the inner surfaces  113 ,  115  of the end portions  112 ,  114 , respectively, against the surface of the glass balls to make the seam waterproof while preventing an electrical short circuit between the cathode  108  and anode  110 . The glass or fiber balls  118  do not absorb moisture and thus do not allow water to enter the battery. Optionally, a water-resistant composite material or thin layer of silicon  120  may be used to fill the interstitial voids between the glass balls. 
     FIG. 5 is a fragmentary top plan view of the flexible battery structure illustrated in FIG. 4 as viewed from the cathode side  108 . The marginal peripheral seam having a length L surrounds the periphery of the battery structure  100 . 
     Referring now to FIG. 6, a schematic cross-section of another alternate embodiment of the flexible battery structure embodying the present invention is illustrated therein and is generally designated  200 . The battery structure  200  includes a cathode  202 , cathode active material layer  204 , electrolyte or separating layer  206 , anode active material layer  208  and an anode  210 . The construction of the battery structure of FIG. 6 is similar to that shown in FIG. 4, with the exception that a caliber  212  made of a water-resistant material is inserted between the overlapping end portions  214  of the cathode substrate  202  and the end portion  216  of the anode substrate  210  defining the marginal peripheral seam. A water-resistant composite material  218  may also be inserted into the marginal peripheral seam along with the caliber  212  and the end portions  214 ,  216  are squeezed under pressure during manufacture to ensure that the water-resistant composite material  218  completely fills the space between the end portions to provide the necessary waterproof seal. 
     Turning now to FIG. 7, a schematic cross-section of the flexible battery illustrated in FIG. 6 is shown in one possible connection arrangement with an external electrical circuit. The battery  200  is inserted in the direction indicated by the direction arrow  250  into an electrical connector, generally designated  252 . The connector has a spring contact  254 , which comes into electrical and mechanical contact with the cathode  202  end portion  214  when the battery  200  is inserted into the socket  252 . A second spring contact  256  is mounted and carried by the socket  252  and comes into contact with the surface of the end portion  216  of the anode  210  when the battery structure  200  is inserted into the socket. Electrical conductors  258 ,  260  are connected to the spring contacts  254 ,  256 , respectively, and lead to the external electrical circuit with which the battery structure  200  operates. 
     It is to be understood that the present invention is not to be considered as limited to the specific embodiments described above and shown in the accompanying drawings, which merely illustrate the best mode presently contemplated for carrying out the invention, and which is susceptible to such changes as may be obvious to one skilled in the art, but rather that the invention is intended to cover all such variations, modifications and equivalents thereof as may be deemed to be within the scope of the claims appended hereto.