Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-03-06
2001-02-13
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S217000, C429S218100, C429S231100, C429S231800, C429S345000
Reexamination Certificate
active
06187479
ABSTRACT:
A rechargeable battery or cell is disclosed in which the electrode active material consists of at least one nonmetallic compound or salt of the electropositive species on which the cell is based (e.g., Li
+
, Na
+
) and the electrolyte or electrolyte solvent consists predominantly of a halogen- and/or chalcogen-bearing covalent compound such as SOCl
2
or SO
2
Cl
2
. Also disclosed are cell component materials which include electrodes that consist primarily of salts of the cell electropositive species and chemically-compatible electrolytes. These latter electrolytes include several newly-discovered ambient temperature molten salt systems based on the AlCl
3
—PCl
5
binary and the AlCl
3
—PCl
5
—PCl
3
ternaries.
BACKGROUND OF THE INVENTION
This invention relates to ambient temperature, rechargeable, non-aqueous, all-inorganic electrochemical cells. More specifically, this invention relates to such cells utilizing a new type of electrode in which the active material consists entirely of one or more nonmetallic compounds or salts of the electropositive species on which the cell is based (e.g., Li
+
, Na
+
), which is typically the same as that of the main charge-carrying species in the electrolyte. In addition, this invention relates to ambient temperature, non-aqueous, inorganic electrolytes for use in cells based on this new electrode type.
The ultimate goal of the research underlying the present invention is to develop improved rechargeable batteries operating at or near room temperature that provide high specific energy and power densities suitable for electric vehicles. To allow for a wide range of ambient conditions, the desired temperature range for electric vehicle batteries as envisioned in the long term by the U.S. Advanced Battery Consortium (USABC) is −40 to 85° C. At present, the lead-acid battery is the leading candidate for full-scale on-the-road electric vehicles due to its mature yet continually evolving technology and well-established manufacturing base. Its chief limitation, however, is a low specific energy which stems from a low cell voltage due to its use of aqueous electrolytes and the relatively high cell component material molecular or formula weights. Thus, worldwide efforts have been in progress to develop alternate battery chemistries that provide higher specific energy and power densities as required to insure the long term economic viability of electric vehicles.
Lithium is among the most promising of rechargeable battery electrode active materials because of its high standard potential and low electrochemical equivalent weight. For many years, ambient temperature rechargeable lithium batteries have been in an ongoing state of research and development to provide lightweight, economical power sources for a variety of applications ranging from notebook computers and heart pacemakers to full-scale aerospace and transportation needs. A recent review of all the different approaches taken to date in the design of ambient temperature rechargeable lithium batteries is provided by Hossain (Chap. 36 in
Handbook of Batteries
, 2nd ed., ed. by D. Linden, McGraw-Hill, Inc., 1995).
From a review of the patent literature and other published studies pertaining to advanced batteries considered for use in electric vehicles, it appears that the majority of research in ambient temperature lithium rechargeable batteries has been concentrated almost exclusively on two main types of cells which differ according to the form the lithium active material assumes during cell operation, i.e., i) those using lithium metal anodes, or ii) those using certain solid materials for both electrodes that can reversibly intercalate Li
+
cations. Both types of cells may utilize a variety of liquid or solid (e.g., polymer) electrolytes. In type (ii) cells, often referred to as Li-ion (“lion”) cells, Li
+
cations are shuttled back and forth between the electrodes during charging and discharging, and no free lithium metal is present. Li-ion cells often utilize porous carbon at the anode and lithiated first row transition metal oxides (e.g., Li
x
MnO
2
) at the cathode, but many deviations from this basic design exist, e.g., certain lithiated transition metal compounds with potentials sufficiently close to that of metallic lithium (e.g., Li
x
WO
2
) may be used as anodes, or porous carbon electrodes may be used at both the cathode and anode, each differing in the amount of surface area. Much research has and continues to be devoted to the development of new (and/or to the improvement of existing) materials with enhanced Li
+
ion intercalation storage capabilities. At present, however, neither lithium metal anode nor Li-ion cells are sufficiently developed for large-scale commercial use in electric vehicle batteries. For lithium metal anode batteries, safety problems associated with metal dendrites abound, and for Li-ion-type batteries, current limitations regarding long-term storage and specific energy and power density need to be overcome.
The present invention, which makes use of all-metal salt electrodes, is a significant departure from conventional battery designs. A review of the prior art shows that there are relatively few designs using lithium and other lightweight, electropositive metals in which the electrode active metal assumes the form of a distinct salt phase during some stage of cell operation. U.S. Pat. No. 4,154,902 by Schwartz describes both primary and rechargeable ambient temperature, non-aqueous cells in which, during the charging stage, the electrode active material is in the form of a dithionite salt of an alkali or alkaline earth metal. In the cell design of Schwartz, the dithionite salt (e.g., Li
2
S
2
O
4
) is dissolved in a suitable anhydrous solvent together with another salt of the same metal with a higher solubility (e.g., LiClO
4
) to enhance the electrolyte metal cation conductivity, and SO
2
is usually added at saturation. During charging, the electrode active metal is deposited in metallic form at the anode and SO
2
is produced at the cathode. During discharging, the dithionite salt is reformed from metal cations produced at the anode by oxidation of the metal and S
2
O
4
2−
anions produced at the cathode upon reduction of SO
2
. Throughout cell operation, a steady supply of dithionite salt is provided by the battery design which employs a system for forced circulation of the electrolyte.
It is well known that in primary lithium metal anode cells employing SO
2
as the cathode active material, lithium dithionite salt, which has a low solubility in SO
2
as well as in most other electrolyte solvents, is typically formed during cell discharge and is deposited as an electronically insulating layer (but with some ionic conductivity) on the cathode current collector or substrate. Cell failure in such systems often occurs when the cathode current collector is entirely or almost entirely covered with solid Li
2
S
2
O
4
. Under these conditions, further cell operation is not possible, and cells in which the cathode current collector is coated with solid Li
2
S
2
O
4
are generally not considered to be rechargeable.
Schwartz's invention is of interest in that it teaches that it is possible to utilize the reaction product of spent anode active metal and cathode depolarizer (i.e., dithionite salt) as an electrode active material in rechargeable cells, at least in some systems. However, Schwartz's invention differs fundamentally from the present invention in that the anode active metal is not always present in oxidized form but rather undergoes repeated oxidation and reduction during cell cycling (as in all metal anode cell designs). Also, the electrode active metal dithionite salt appears to be utilizable in Schwartz's cells only in the form of an electrolyte solute, and no dithionite (or other) salt phase is deposited in solid form at either electrode at any stage of cell operation.
Another important aspect in which the present invention differs from that of Schwartz is that, in the latter invention,
Kalafut Stephen
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
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