Flexible battery structure

Abstract: A flexible battery structure (50) comprises a stack of a layer of cathode active material (58) and anode active material (62) separated by a layer of electrolyte (60) and held between a cathode flexible substrate (52) and an anode flexible substrate (64), 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 (74,76) which are hermetically sealed with a water-resistant composite material (80). The outer surface of the cathode (54) and outer surface of the anode (66) form the positive polarity and negative polarity connection leads of the battery structure. The anode and cathode substrates (52,64) 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. Japanese Patent Publication No. JP 62055866 describes a thin cell that is insulatively sealed using a hot melt adhesive mixed with inorganic beads. 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, there is provided a flexible battery structure according to claim 1. Preferred embodiments of the invention are set out in the dependent claims. Other features and advantages of the present invention will become more apparent from the following detailed description of presently preferred embodiments of the invention when considered in conjunction with the accompanying drawings. Brief Description of the Drawings FIGURE 1 is a schematic cross-section of a representative polymer battery. FIGURE 2 is a schematic cross-section of a flexible battery embodying the present invention. FIGURE 3 is a fragmentary top plan view of the flexible battery of FIG. 2. FIGURE 4 is a schematic cross-section of an alternate embodiment of a flexible battery embodying the present invention. FIGURE 5 is a fragmentary top plan view of the flexible battery of FIG. 4. FIGURE 6 is a schematic cross-section of another alternate embodiment of a flexible battery embodying the present invention. FIGURE 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. 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.

Claims: A flexible battery structure (100) comprising: a first flexible substrate (108) defining a cathode; a second flexible substrate (110) defining an anode; the first and second flexible substrates (108, 110) having surfaces to provide a positive polarity and negative polarity connection lead, respectively; a stack of layers sandwiched between the first and second flexible substrates (108, 110), the stack comprising a cathode active material layer (102), an electrolyte layer (104) and an anode active material layer (106), wherein the first and second flexible substrates (108, 110) extend beyond the periphery of the stack; a retaining wall at the edge of the stack for containing the stack; and a hermetic seal arrangement disposed at least partly between the first and second flexible substrates (108, 110) for preventing moisture coming into contact with the stack, wherein the hermetic seal arrangement includes one or more glass or fibre balls (118). A flexible battery structure according to claim 1, wherein the balls (118) are pressed between the first and second substrates (108, 110). A flexible battery structure according to claim 1, wherein the hermetic seal arrangement comprises a non-electrically conductive, water-resistant composite material (120). A flexible battery structure according to claim 1, wherein the first and second flexible substrates (108, 110) are arranged in a spaced relationship to prevent an electrical short circuit between the first flexible substrate and the second flexible substrate. A flexible battery structure according to claim 1, wherein the first and second flexible substrates (108, 110) are metal foil. A flexible battery structure according to claim 5, wherein the first flexible substrate (108) is copper. A flexible battery structure according to claim 5, wherein the second flexible substrate (110) is aluminium. A flexible battery structure according to any one of claims 5 to 7, further comprising a thin layer of silicon (120) between the first and second flexible substrates. A flexible battery according to claim 1, wherein the electrolyte layer (104) further comprises means for separating said cathode active material layer (102) and said anode active material layer (106).

Inventors: NASKALI MATTI, NASKALI, MATTI
Applicants: NOKIA CORP, NOKIA CORPORATION
Application year: 2001
Main classification: H01M10
IPC codes: H01M2, H01M10, H01M4