Abstract:
Disclosed is a paper battery that includes a cellulosic substrate having absorbed thereon an electrolyte material and first and second barrier substrates disposed on opposite sides of the cellulosic substrate. Each of the first and second barrier substrates have an electrode printed thereon. At least one of the first and second barrier substrates includes first and second polymer layers. Further disclosed is a method of manufacturing a paper battery that includes the steps of absorbing an electrolyte material onto a cellulosic substrate and disposing on opposite sides of the cellulosic substrate first and second barrier substrates. Each of the first and second barrier substrates have an electrode printed thereon. At least one of the first and second barrier substrates includes first and second polymer layers.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to U.S. provisional application Ser. No.: 61/771,207, filed on Mar. 1, 2013, the contents of which are herein incorporated by reference in their entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure generally relates to batteries and methods of manufacturing batteries. 
       BACKGROUND 
       [0003]    A “paper battery” is known in the art as a thin electric battery that employs a substrate that is formed largely of cellulose. Paper batteries are thin, flexible, and environment-friendly, which allows for their integration into a wide range of products. Paper batteries function in a manner that is analogous to conventional chemical batteries, but with the difference that paper batteries are non-corrosive and do not require a bulky housing. Exemplary uses for paper batteries include radio frequency identification (RFID) devices, medical diagnostic equipment, and drug delivery transdermal patches. 
         [0004]    Paper batteries are manufactured by absorbing an electrolyte onto a cellulose substrate. The electrolyte is moisture absorbing, especially when the paper battery is used in a high temperature and/or high humidity application. Any water ingress into the cellulose substrate causes a marked decrease in battery performance. To help protect the battery against moisture intrusion, and to maintain the flexibility of the battery, thin plastic films such as polyethylene terephthalate (PET) with an aluminum coating are adhered to the battery as an exterior packaging layer and as a “barrier” layer against moisture. The PET/aluminum films are also used as a substrate to “print” the battery electrodes thereon using a conductive ink. 
         [0005]    Paper batteries currently known in the art suffer from several drawbacks. The aluminum coated PET film barrier layer, which is often deposited via physical vapor deposition (PVD), does not provide a sufficient moisture barrier due in part to “pin holes” and scratch defects, which allow moisture to pass therethrough. Further, the aluminum coating has an electromagnetic shield effect, which is not favorable in many applications, such as RFID devices, where electromagnetic transmission is desirable. 
         [0006]    As such, it would be desirable to provide improved paper batteries and methods for manufacturing paper batteries that have increased moisture resistance and that are not electromagnetically shielded. Further, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter. 
       BRIEF SUMMARY 
       [0007]    In one exemplary embodiment, disclosed is a paper battery that includes a cellulosic substrate having absorbed thereon an electrolyte material and first and second barrier substrates disposed on opposite sides of the cellulosic substrate. Each of the first and second barrier substrates have an electrode printed thereon. At least one of the first and second barrier substrates includes first and second polymer layers. 
         [0008]    In another exemplary embodiment, disclosed is a method of manufacturing a paper battery that includes the steps of absorbing an electrolyte material onto a cellulosic substrate and disposing on opposite sides of the cellulosic substrate first and second barrier substrates. Each of the first and second barrier substrates have an electrode printed thereon. At least one of the first and second barrier substrates includes first and second polymer layers. 
         [0009]    In yet another exemplary embodiment, disclosed is a paper battery that includes a cellulosic substrate having absorbed thereon an electrolyte material that includes zinc chloride and first and second barrier substrates disposed on opposite sides of the cellulosic substrate. Each of the first and second barrier substrates have an electrode printed thereon. The electrode of the first barrier substrate includes zinc and the electrode of the second barrier substrate includes manganese dioxide. At least one of the first and second barrier substrates includes first and second polymer layers. The first polymer layer includes poly-cholortrifluoroethylene and the second polymer layer includes polyethylene terephthalate. Further, the first and second polymer layers are laminated or co-extruded together. 
         [0010]    This brief summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0012]      FIG. 1  illustrates the structure of a paper battery, in cross-section, as is currently known in the art. 
           [0013]      FIG. 2  illustrates the structure of a paper battery, in cross-section, in accordance with an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding Technical Field, Background, Brief Summary, or the following Detailed Description. 
         [0015]    Embodiments of the present disclosure are broadly directed to paper batteries and methods of manufacturing paper batteries.  FIG. 1  illustrates the structure of a paper battery, in cross-section, as is currently known in the art. Certain of the layers  101 - 106  depicted therein are shown separated from (non-adjacent to) one another for ease of illustration; however, it will be appreciated that in practice the layers  101 - 106  are adhered to one another to form an integrated and functioning battery. 
         [0016]    The paper battery depicted in  FIG. 1  generally includes at least a first electrode  103  including a first electrochemical layer (e.g., a cathode), a second electrode  105  including a second electrochemical layer (e.g., an anode), and an electrolyte disposed on a cellulosic substrate  104  that interacts with the electrodes to create an electrical current. All of the first and second electrodes ( 103 ,  105 ) and the electrolyte on the substrate  104  are typically contained between two or more barrier substrates  102 ,  106 , which provide a substrate on which to “print” the electrodes  103 ,  105 , as well as provide electrical isolation from the electrode and a moisture barrier to prevent moisture intrusion upon the electrolyte. 
         [0017]    Regarding the first and second electrodes  103 ,  105 , the deposition of the electrodes on respective barrier substrates  102 ,  106  can be accomplished by, for example, printing conductive and/or electrochemical inks and/or laminating a metallic foil, such as a zinc foil, for example, on one or more high-speed web printing presses with rotary screen and/or flexographic printing stations. Other suitable methods include web printing with flat-bed screens or a sheet-fed flat-bed printing press. A suitable material for use as the cathode  103  includes manganese dioxide (MnO 2 ). A suitable material for use as the anode  105  includes zinc. Other formulations of the cathode or anode may be used as are known in the art. 
         [0018]    The cellulosic substrate  104  may be prepared from cellulosic fibers derived from wood pulp. Exemplary cellulosic fibers include, but are not limited to, those derived from wood, such as wood pulp, as well as non-woody fibers from cotton, from straws and grasses, such as rice and esparto, from canes and reeds, such as bagasse, from bamboos, from stalks with bast fibers, such as jute, flax, kenaf, cannabis, linen and ramie, and from leaf fibers, such as abaca and sisal. It is also possible to use mixtures of one or more cellulosic fibers. The cellulosic substrate  104  is immersed in an electrolyte solution to absorb the electrolyte solution on to the cellulosic substrate  104 . Zinc chloride (ZnCl 2 ) in solution is an exemplary electrolyte, and can be used in the concentration range of about 18%-45% by weight, for example. Other suitable electrolyte formulations, such as ammonium chloride (NH 4 Cl), mixtures of zinc chloride (ZnCl 2 ) and ammonium chloride (NH 4 Cl), zinc acetate (Zn(C 2 H 2 O 2 )), zinc bromide (ZnBr 2 ), zinc fluoride (ZnF 2 ), zinc tartrate (ZnC 4 H 4 O 6 ), zinc per-chlorate Zn(ClO4) 2 ), potassium hydroxide, sodium hydroxide, or organics, for example, could also be used. 
         [0019]    The barrier substrates  102 ,  106  on which the electrodes  103 ,  105  are printed can be formed of a plastic film of, for example, a polypropylene or a polyethylene. In order to improve the moisture barrier properties of the barrier substrates  102 ,  106 , one or more of the barrier substrates  102 ,  106  can be provided as a metallized film. The term metallized film refers to a polymer film layer with a metal layer coated thereon. As shown in  FIG. 1 , barrier substrate  102  includes a metal layer  101  disposed thereover. Examples of a suitable metallized film include metallized polyethylene teraphthalate (MPET) and metallized polypropylene (MPP). An exemplary metal for use as the metal coating layer  101  includes aluminum (Al). 
         [0020]    As noted previously, when a metallized barrier substrate is employed, “pin hole” and scratch defects can occur in the metal coating, which allows moisture to pass therethrough. Further, the metal layer  101  has an electromagnetic shield effect, which is not favorable in applications where electromagnetic transmission is desirable. As such, embodiments of the present disclosure are directed to an improved paper battery structure that provides the increased moisture resistance of a metallized plastic/polymer film coating, but does not suffer the manufacturing and transmission shielding drawbacks that are commonly encountered in the paper batteries currently known in the art, as in  FIG. 1 . 
         [0021]    Reference is now made to  FIG. 2 , which illustrates the structure of a paper battery, in cross-section, in accordance with an exemplary embodiment of the present disclosure. As with  FIG. 1 , certain of the layers  201 - 206  depicted therein are shown separated from (non-adjacent to) one another for ease of illustration; however, it will be appreciated that in practice the layers  201 - 206  are adhered to one another to form an integrated and functioning battery. 
         [0022]    As shown in  FIG. 2 , layers  203 - 206  are substantially the same as layers  103 - 106 , respectively, described above with regard to  FIG. 1  (that is, layer  203  is a first electrode, e.g., a cathode, layer  204  is a cellulose substrate with an electrolyte absorbed thereon, layer  205  is a second electrode, e.g., an anode, and layer  206  is a polymeric barrier substrate). Rather than employing a metallized plastic/polymer layer (e.g.,  101 ,  102  of  FIG. 1 ) for protection against moisture intrusion and for a substrate on which to print the first electrode, embodiments of the present disclosure utilize first and second polymer layers  201 ,  202 . In an exemplary embodiment, the second polymer layer  202  is formed of PET, which as noted above provides moisture barrier protection, and also serves as a substrate on which to print the electrode. The first polymer layer  201  is formed of poly-chlorotrifluoroethylene (poly-CTFE or PCTFE). In an alternative embodiment, the first polymer layer  201  is formed of poly-vinylidenechloride (poly-VDC or PVDC). In one embodiment, the first and second polymer layers  201 ,  202  may be formed together by lamination or co-extrusion. In another embodiment, layer  201  may be provided as a heat-sealable PCTFE barrier layer to adhere to layers  202  and/or  206 . In yet another embodiment, the entire battery device may be encapsulated by a PCTFE encapsulant layer (not shown), thus layer  201  can be formed continuously around the entire device. In one embodiment, the thickness of the first and second polymer layers (laminated or co-extruded together) can range from about 25 microns to about 500 microns, for example from about 50 microns to about 300 microns. 
       ILLUSTRATIVE EXAMPLE 
       [0023]    The present disclosure is now illustrated by the following non-limiting example. It should be noted that various changes and modifications can be applied to the following example and processes without departing from the scope of this invention, which is defined in the appended claims. Therefore, it should be noted that the following example should be interpreted as illustrative only and not limiting in any sense. 
         [0024]    A barrier substrate was prepared in accordance with  FIG. 2 , utilizing PCTFE as the first polymer layer and PET as the second polymer layer. The first and second polymer layers were laminated together. The combined thickness of the first and second polymers layers, after lamination, was about 280 microns. 
         [0025]    A barrier substrate as is used on the SoftBattery® paper battery, which includes an aluminum coating PET substrate barrier layer as in the prior art example of  FIG. 1 , was commercially obtained from Enfucell Corporation of Vantaa, Finland for purposes of comparison. Measurements of this barrier substrate indicated that the aluminum coated PET substrate barrier layer was about 50 microns thick. 
         [0026]    Both the prepared barrier substrate and the comparison barrier substrate were exposed to an atmosphere of  40 ° C. and 75% relative humidity. Moisture intrusion in the prepared barrier substrate was measured at 0.50 g/m 2 /day. Moisture intrusion in the commercially obtained comparison barrier substrate was measured at 5.50 g/m 2 /day. 
         [0027]    As such, it has been surprisingly discovered by the inventors herein that a paper battery manufactured with first and second polymer layers as a barrier substrate (for example PCTFE and PET or PVDC and PET), in place of a metallized plastic film (for example Al coated PET), provides increased protection against moisture intrusion. Further, as the disclosed paper battery does not use a metal layer or a metal coating, blocking of electromagnetic transmissions is substantially avoided. The first and second polymer layers can be easily co-extruded with one another or laminated to one another, thereby providing a simple and cost-effective manufacturing process. 
         [0028]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the inventive subject matter, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the inventive subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the inventive subject matter. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the inventive subject matter as set forth in the appended claims.