The need for information cards that contain electronics such as integrated circuits (IC) has been increasing as of late. The IC can provide functions, such as for retrieving, processing, transmitting and storing information. Such cards are generally referred to as “smart cards” which have potential application in a wide range of fields, including commerce, transportation, communication, identification, and security.
It is known to incorporate batteries into cards to provide a power source for the electronic circuitry within. Having a battery incorporated into the IC card allows for the storage of greater amounts of data, and further allows for improved processing capabilities.
Because of the difficulty of providing the energy required for most applications within the space constraints of a typical credit card, it is desirable to use battery types which provide the highest energy density. Lithium batteries have been introduced into the market because of their high energy densities. Lithium is atomic number three on the periodic table of elements, having the lightest atomic weight and highest energy density of any solid material. As a result, lithium is a preferred material for batteries, having very high energy density. Lithium batteries are also desirable because they have a high unit cell voltage of up to approximately 4.2 V, as compared to approximately 1.5 V for both Ni—Cd and Ni-MH cells. Lithium batteries can be either lithium ion batteries or lithium metal batteries. Lithium ion batteries intercalate lithium ions in a host material, such as graphite, to form the anode. On the other hand, lithium metal batteries use metallic lithium or lithium alloys for the anode.
Lithium batteries having solid polymer electrolytes represent an evolving alternative to lithium batteries having liquid electrolytes. Solid polymer electrodes are generally gel type electrolytes which trap solvent and salt in pores of the polymer to provide a medium for ionic conduction. Typical polymer electrolytes comprise polyethylene oxide (PEO), polyether based polymers and other polymers which are configured as gels, such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and polyvinylidine fluoride (PVDF). The polymer electrolyte generally functions as a separator, being interposed between the cathode and anode films of the battery.
Lithium metal polymer (LMP) rechargeable batteries offer improved performance as compared to Li ion batteries, particularly higher capacity. LMP batteries result from the lamination/assembly of three types of main thin films: a film of positive electrode comprising a mixture of a polymer and an electrochemically active material such as lithium vanadium oxide, an electrolyte film separator made of a polymer and a lithium salt, and a negative electrode film comprising metallic lithium or a lithium alloy.
Unfortunately, conventional batteries including lithium metal or lithium ion batteries lack the stability to be subjected to credit card processing, which can include a temperature of 125C to 140C, a pressure of 200 to 250 psi, and a dwell time of 5 to 15 minutes. Conventional batteries subjected to the above described card lamination conditions will generally either catastrophically fail or experience a large shift in operating parameters which would render them of no practical use. As a result, although batteries have been disposed inside credit cards, a low temperature glue has been used to bind the battery to the card.