Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1999-09-02
2003-12-16
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S306000, C429S309000, C429S310000, C429S312000, C429S313000, C429S314000, C429S316000, C429S319000, C429S320000, C429S321000, C429S322000, C429S323000, C429S233000, C429S234000, C429S162000, C029S623100, C029S623300, C029S623500
Reexamination Certificate
active
06664006
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the manufacture of solid state electrochemical cells, particularly high energy density cells having very thin electrode and electrolyte structures for building ultra-thin laminar batteries. The invention also relates to lithium polymer electrolyte batteries containing such electrochemical cells and to their methods of making.
2. Description of the Related Art
Lithium rechargeable batteries are the focus of intense investigation around the world because of the rapid proliferation of portable electronic devices in the international marketplace. The state-of-the-art lithium battery is a lithium ion battery which uses a carbon electrode as the negative electrode or anode and a lithiated metal oxide, such as lithiated cobalt oxide, lithiated nickel oxide, lithiated manganese oxide, or mixtures of these materials as the positive electrode or cathode, a microporous polypropylene or polyethylene separator that separates the two electrodes and prevents them from shorting electrically, and liquid organic solvents containing a lithium salt as the electrolyte. The electrolyte is usually absorbed into the separator material and provides high ionic conductivity (10
−
to 10
−2
S/cm) and migration of ions between the electrodes of the cell. These batteries are commercially available and are commonly used in portable computers, cellular telephones and camcorders among other applications. The specific energy and energy density of the lithium ion battery is usually about 125 Wh/kg and 260 Wh/l. Usually, the packaged battery (in a hard plastic case) has a much lower energy density than the:individual cell (20% lower). The cycle life (number of times the battery can be recharged) of this battery is about 500 to 800 cycles, the self-discharge (i.e. loss of capacity on standing) per month is about 10%, and cost is about $1 per Watt-hour of energy. These batteries can be manufactured at a high rate of speed. Even though this battery technology is being commercialized very heavily, there have been numerous safety questions. Cells that have been abused under crush test or high temperature test have been known to explode and catch fire.
An offshoot of the above system is the lithium ion polymer electrolyte battery. The electrode chemistry is the same, but the liquid electrolyte (up to 70% by weight of the electrolyte) in this case is absorbed in a polymer membrane instead of the microporous polypropylene separator. It is based on the Bellcore's U.S. Pat. No. 5,296,318 utilizing a polyvinylidene fluoride (PVDF) polymer as the medium that absorbs the electrolyte solvent. Ironically, PVDF is non-conducting and so its sole function is to hold the liquid organic solvent(s) in its structure in a manner similar to a sponge holding water. Because the technology uses an electrolyte solvent absorbed in a polymer, it is not easy to manufacture cells in high speed. Automation of this technology may be very difficult. It is believed the energy densities (gravimetric and volumetric) for this type of battery are lower than the existing lithium ion batteries, cycle life is not too impressive, and cell cost is several dollars per Watt-hour. The physical forms the lithium ion polymer cell could take was a heavily touted feature, but today only flat prismatic cells are typically manufactured.
Another rechargeable lithium battery system uses a lithium metal as the negative electrode instead of carbon, and so the energy density of this system can be increased tremendously because of the very high specific capacity of metallic lithium compared to carbon. Gravimetric specific energy density as high as 200 to 250 Wh/kg have been reported in the literature for rechargeable lithium metal batteries. Lithium metal anode batteries are not new. Primary, non-rechargeable batteries using lithium metal, non-aqueous organic electrolytes and a positive electrode have been used in many applications for the past 25 years despite the fact that lithium metal is thermodynamically unstable in liquid organic solvents and reacts with the solvent irreversibly. Secondary batteries using lithium metal as the negative electrode, intercalation or insertion compounds as the positive electrode, and non-aqueous organic electrolytes were the focus of intense investigation during the 1970's and 1980's. However, the problem with using lithium in a rechargeable system is that because of the instability of lithium in these solvents, a large excess of lithium is required to off-set the chemical reaction of lithium with the solvent, usually as much as 3 to 5 fold. In addition, the cycle life of lithium metal batteries in organic solvent electrolytes is less than 200 cycles. Lithium plating and stripping during the charge and discharge cycles creates a porous deposit of very high surface area and increased activity of the lithium metal with respect to the electrolyte. The reaction is highly exothermic and the cell can vent with flame if heated or short-circuited. Much effort has been expended to improve the cycling efficiency of the lithium anode through changes to the electrolyte or investigating alloys of lower lithium reactivities. Safety features such as fusible separators which cease the electrochemical reactions when the battery temperature approaches a critical value and overcharge protection redox couples have also been incorporated to improve the safety of these cells.
In addition, liquid solvent electrolyte in any of the above cell systems is often corrosive and toxic and presents handling difficulties through spillage or leakage from the cell. It can also outgas during overcharge or overdischarge or at elevated temperatures, leading to safety problems. Most of the problems have been associated with the electrode/electrolyte interface.
In order to overcome the disadvantages inherent in liquid electrolytes and to obtain superior long-term storage stability there is interest in solid polymeric electrolytes in which ion mobility is achieved through coordination by sites on the polymer chain of electrolyte ions, thus promoting electrolyte dissolution and salt dissociation. An all-solid-state battery using an ionically conductive polymer membrane as the electrolyte would have several attractive features. It could be made into virtually any shape and size, be reasonably rugged and leakproof, and would have low self-discharge. It could be made into thin film power cells or thick film energy cells, would have high open-circuit potentials using a lithium anode, and could be produced by automated fabrication techniques. These features represent a unique combination of properties and give rise to the possibility of using such batteries, as either secondary or primary devices across a wide range of applications.
One polymer that has been examined extensively for use in a solid state battery is poly(ethylene oxide) or PEO, which is able to form stable complexes with a number of salts. Because of its low ionic conductivity at ambient temperature of about 10
−9
to 10
−8
S/cm, batteries examined using this material had to operate at 100° C. and above. A major problem with PEO based electrolytes at temperatures below 60° C. is their high crystallinity and the associated low ion mobility. In recent years a number of radically different approaches have been taken to improve the conductivity of PEO and PEO-based polymers that have also led to the proposal of other polymers. These approaches included, polymer modifications and synthesizing new polymers; forming composite polymers with ceramic materials; using plasticizer salts to increase the ion transport and mobility of the cation; using plasticizing solvents in the polymer again to increase the ionic character of the cation; among other approaches. Several review articles describe these approaches in detail, e.g. “Technology Assessment of Lithium Polymer Electrolyte Secondary Batteries” by M. Z. A. Munsh
Conley & Rose, P.C.
Crepeau Jonathan
Gulakowski Randy
Lithium Power Technologies, Inc.
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