Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Flat-type unit cell and specific unit cell components
Reexamination Certificate
2003-03-17
2004-10-19
Crepeau, Jonathan (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Flat-type unit cell and specific unit cell components
C429S231100, C429S231200, C429S231950, C429S322000, C029S623100, C029S623500, C205S059000
Reexamination Certificate
active
06805999
ABSTRACT:
TECHNICAL INVENTION
This invention relates to the fabrication of lithium thin film secondary batteries.
DISCLOSURE OF INVENTION
Batteries are galvanic electrochemical cells which store and supply electrical energy as a product of a chemical reaction. In their simplest conceptualization, batteries have two electrodes, one that supplies electrons by virtue of an oxidation process occurring at that electrode, termed the anode (hereinafter, “anodic processes”), and a second one that consumes electrons by virtue of a reduction process occurring at that electrode, termed the cathode (hereinafter, “cathodic processes”).
There are two broad classifications of batteries, primary batteries and secondary batteries. In primary batteries, either the anodic process, or the cathodic process, or both are irreversible, as defined for electrochemical processes. For this reason, once the reagents participating in the reactions are by-and-large consumed, the battery can't be returned to a charged state by electrochemical means.
In secondary batteries the electron producing and consuming reactions are for the most part reversible, as defined for electrochemical processes, and therefore such a battery can be cycled between a charged and discharged state electrochemically.
The reactions employed in batteries to produce and consume electrons are redox reactions. A pair of such reactions is called a redox couple. Each redox reaction is termed a half cell, with two half cells constituting a simple battery when the half cells are placed in ionic communication such that voltage potential appears between the electrodes of the half cells. Typically, the electrodes of several sets of half cells are electrically coupled together in either series or parallel configuration to supply a greater voltage or a greater current, or both than that which is available from a single set of half cells.
The voltage potential of a simple battery (a single set of half cells) is fixed by the set of redox couples chosen to produce and consume electrons. The redox couples are chosen such that the potential energy of the electron producing reaction yields electrons of sufficient potential energy to supply electrons to the electron consuming reaction. The electromotive force (emf) supplied by the battery is the difference between the potential energy of the electrons produced by the electron producing reaction and that required of the electrons consumed by the electron consuming reaction. As electrons are transferred from the electron producing reaction to the electron consuming reaction, charge within the half cells in which these reactions are carried out is balanced by the movement of ions between the half cells.
Ion batteries utilize materials in their construction that exhibit low resistance to ion movement through and within their structure. Thus, ion batteries improve the efficiency of storing and transferring electrical energy by reducing the resistance that ions must overcome at the interfaces of the various phases within the battery, and improve energy storage capacity by utilizing materials which do not polarize, and therefore during charge movement do not build up space charge regions which contribute resistance to charge movement within the battery. This feature tends to permit a higher density of charge species to be moved within a given volume of an ion battery than is possible with conventional materials. Additionally, thin film techniques permit the formation of very thin electrolyte layers separating the redox couples, further reducing resistance to charge movement within the battery structure. Thin film ion batteries hold the promise of much higher energy densities than are possible from conventional wet chemistry batteries.
Ion batteries can be prepared from macroscopic compounding techniques to fabricate anode, cathode, and electrolyte materials which are then bonded together to form the battery (the so called “thick film” technique), or by depositing thin films of such materials using vacuum techniques, producing “thin film” batteries. The fabrication of batteries by “thick film” techniques is usually directed toward high current capacity devices. Thin film batteries are generally employed in low current draw applications in which space and weight must be conserved.
U.S. Pat. No. 5,895,731 (hereinafter “the '731 patent) to Clingempeel is exemplary of batteries fabricated using “thick film” construction. The '731 patent teaches the preparation of a cathode from a mixture of powders of titanium nitride, selenium, silicon, and buckminsterfullerene bonded together with epoxy polymer to aluminum foil. Additionally the '731 patent teaches the preparation of an anode from lithium foil, fiberglass matting and n-methyl-pyrrollidone, and the preparation of an electrolyte layer by gelation of a mixture of n-methyl-pyrrollidone, lithium metal, and polyimide powder to produce a cross-linked lithium gel electrolyte which is cast into a sheet. These materials are pressed together and sealed in polyimide plastic with appropriate electrical contacts to the anode and cathode. Production of such a battery requires strict atmospheric control during fabrication to exclude moisture and oxygen, and numerous preparatory steps.
Thin film battery fabrication techniques are well known to those skilled in the art. Thus, for example, U.S. Pat. No. 5,338,625 to Bates (hereinafter “the '625 patent”), teaches the formation of a lithium based thin film battery by vacuum deposition of two co-planar vanadium current collectors on an insulating substrate. Upon one of the current collectors is deposited a cathode comprising an amorphous vanadium oxide layer. This cathode layer is deposited by reactive ion sputtering from a vanadium target in an oxygen environment. On top of the cathode layer is deposited an amorphous lithium phosphorous oxynitride (also called “Sub-stoichiometric lithium phosphorous oxynitride”) layer which acts as an electrolyte. This layer is deposited by reactive ion sputtering of lithium orthophosphate in a nitrogen atmosphere. Finally, a layer of lithium metal was vacuum evaporated onto the assembly, covering both the bare current collector and the current collector bearing the cathode and electrolyte. The disclosed thin film battery contains a bare lithium anode, and as such requires further steps to isolate the anode from the ambient environment. Additionally, because of the presence of the relatively low melting lithium metal the disclosed battery has low tolerance for heating.
Hybrid batteries containing a combination of elements prepared by macroscopic compounding techniques which in turn have thin films deposited onto them have also been described. Thus, U.S. Pat. Nos. 5,569,520 (hereinafter “the '520 patent”)and 5,612,152 (hereinafter “the '152 patent ”), both to Bates, describe a preparation of a lithium manganate cathode pellet using traditional ceramic processing techniques (e.g., hot pressing and sintering the powder). The pellet is then subjected to deposition of a thin electrolyte film of, e.g., lithium phosphorous oxynitride (Sub-stoichiometric lithium phosphorous oxynitride), by reactive ion sputtering using the techniques described above for the '625 patent to Bates. A lithium film anode is then deposited on the exposed face of the electrolyte film, again by vacuum techniques, forming a multilayered thin film battery. The '520 and '152 patents further disclose that an additional mass of lithium can be incorporated into the battery by sandwiching the anode of the multi-layered battery material described above with an additional sheet of lithium foil and cycling the sandwiched construction through several charging/discharging cycles. In this process, the thin lithium film is “plated” onto the foil sandwiched with it to form a continuous phase with the electrolyte/lithium metal interface, bonding the lithium foil into the multi-layered material.
The '152 and '520 patents further disclose that deposition of a lithium anode film on the exposed face of
Lee Se-Hee
Liu Ping
Tracy C. Edwin
Crepeau Jonathan
Midwest Research Institute
White Paul J.
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