Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-12-13
2002-06-11
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
Reexamination Certificate
active
06403255
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to metal-sulfur type cells for making secondary batteries and, particularly to the utilization of organic sulfur as a cathode material for high energy-density batteries.
The utilization of organic sulfur as a cathode material for high energy-density batteries has been of growing interest over the last ten years. While elemental sulfur displays poor electrochemical activity at ambient temperatures, certain organosulfur compounds exhibit pronounced electroactivity that can be harnessed by energy-storage devices.
These organosulfur materials typically contain multiple, thiol groups that can be oxidized readily to form an insoluble high polymer. The polymer backbone is comprised of relatively small organic sections bonded through disulfide bonds. During the reduction process, the disulfide bridges are cleaved to form thiolates and the polymers are scissioned to form anionic monomers. The thiolate ions are reoxidized to form the polymer upon recharging.
U.S. Pat. No. 4,664,991 describes a battery containing a one dimensional electron conducting polymer which forms a complex with at least one polysulfurated chain. This polysulfurated chain is preferably formed through non-covalent interactions, and contains an unknown and uncontrolled, non-stoichiometric amount of sulfur because of the manufacturing process.
U.S. Pat. No. 4,833,048 to Dejonghe et al. describes a battery which features a cathode made from an organic sulfur material. The sulfur-sulfur bonds are broken in the discharged state to form organometallic salts. The organic sulfur material includes a polymer which features sulfur in the backbone, such that the sulfur atoms form disulfide bonds. The patent discloses a cell with an excellent specific charge density. However, although the cathode material in the charged, oxidized form is an insoluble solid, upon discharging the polymer is scissioned to form soluble anionic monomers. The anions, upon formation diffuse from the electrode to the solution. As a result, the charging rate is limited by the rate of diffusion of the thiolate monomers from the bulk solution to the surface of the cathode. Moreover, since the cathode is utilized in the liquid state, solvents are needed to provide the requisite current transport.
One solution for overcoming the deficiencies inherent in cathode materials which are relatively soluble in the reduced, depolymerized state is the utilization of solid electrolytes, i.e., electrolytes that allow the transport of ions as charge carriers, even though the matrix remains solid.
U.S. Pat. No. 5,162,175 to Visco et al. attempts to overcome the deficiencies inherent in cathode materials that are relatively soluble in the reduced, depolymerized state by providing an electrolytic cell in which all the components are in the solid state. In the fully charged states the cathode comprises a one-dimensional, two-dimensional, or three-dimensional polymeric electroactive component. One two-dimensional polymer is disclosed with sulfur groups that are pendant from the backbone, but which is not PVM [poly (vinyl mercaptan)]. Indeed, this polymer has a backbone which also contains nitrogen atoms and which therefore could also be susceptible to scission. Furthermore, U.S. Pat. No. 5,162,175 does not teach or suggest the importance of a polymer backbone which contains only carbon atoms, or of the utility of PVM. It must also be noted that, while U.S. Pat. No. 5,162,175 claims to provide an all solid state battery operating in the temperature range of ambient to 145° C., it is known that the use of solid electrolytes is limited to warm or high temperature cells, at least about 82° C. and certainly no less than about 60° C., because known solid electrolytes, such as polyethylene based electrolytes and &bgr;-alumina based electrolytes, exhibit very low conductivity at ambient temperatures.
U.S. Pat. No. 5,324,599 describes electrode materials, one of which is a conductive polymer with a disulfide group. The conductive polymer is a &pgr; conjugated conductive polymer, which could include the sulfur group either in the backbone or else as a pendant group from the backbone. However, PVM is not a &pgr; electron conjugated conductive polymer. Moreover, PVM has insulating properties and cannot be considered a conductive polymer.
In “Novel Solid Redox Polymerization Electrodes” (JES 138 1896-1901, 1991) Liu et al. classify all the families of polymers based on organic moieties and disulfides. All possible arrangements and all possible polymers of the disulfide family are included. The authors also tested the electrochemical properties of one or more of each of the families and arrived at several important conclusions.
First, cross linked polymers that are cross linked by disulfide bonds suffer from very bad mobility of ions within the polymer film, thus exerting high iR drops.
Second, linear polymers and cross linked polymers that are cross linked by disulfide bonds are suspected of migrating to the anode in the reduced, monomeric state. The authors propose that the synthesis of large polymers may be an appropriate remedy for the problem of migration, which can lead to degradation of the electrolyte or to the deterioration of the anode-electrolyte interface.
Third, ladder polymers are also suspected of migrating to the anode in the reduced state, albeit to a lesser degree. PVM and polyethylene imine derivative are cited as examples of a ladder polymer.
Although PVM is mentioned as an example of a ladder polymer, PVM is not recommended or favored over other ladder polymers, nor are ladder polymers favored over other families of organosulfides. All families of organosulfide compounds are identified by the authors, such that no clear direction is provided.
There are other reasons that the use of PVM in a cathode material is far from obvious. Many characteristics are required for the technical success of an electrolytic cell in general and for a cathode material in particular. These characteristics include:
1. Cyclability/Electrochemical Reversibility
The cyclability of a particular electrolytic cell depends on many factors, the most important of which are the oxidation-reduction characteristics of the cathode in conjunction with the anode and the electrolyte; the tendency of the anions to migrate to the electrolyte or to approach the anode/electrolyte surface during discharging; and the possible degradation of the electrolyte and/or deterioration of the anode/electrolyte interface.
2. Oxidation Potential
The oxidation potential must be high enough to be of practical importance for batteries (>1.5V higher than the anode material), but not too high for the electrochemical window of the cell, which also depends on the behavior of the electrolyte.
3. Specific Charge Density
The specific charge density of a material is an indication of the compactness of energy storage, i.e., the amount of charge delivered by a given species divided by the molecular weight. The specific charge density generally ranges between 20 and 1000 milliamperes*hour/gram.
4. Kinetics of Charge-Transfer Reactions
The rate at which the charge is transferred is of particular importance. Often, the kinetics can be improved significantly by enlarging the contact (surface) areas and/or by utilizing additives with electrocatalytic properties.
5. Self-Discharge
A practical battery must have a reasonable shelf life, i.e., an ability to retain the stored charge over long periods of time when not in use. This depends not only on the particular properties of the cathode and anode materials, but on the interactions with the other components of the cell.
6. Operating Temperature/Temperature Range
Many batteries, particularly solid-state batteries, operate at high temperatures. Batteries using sodium beta alumina as the electrolyte, for example, operate at temperatures above 220° C. The vast majority of battery applications require performance in the range of ambient temperature, from about −20° C. to about 40° C.
7. Sensitivity to specific el
Aurbach Doron
Belostotskii Anatoly M.
Gofer Yosef
Bar Ilan University
Brouillette Gabrielle
Friedman Mark M.
Ruthkosky Mark
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