Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-04-30
2002-10-15
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C423S599000, C423S605000
Reexamination Certificate
active
06465129
ABSTRACT:
BACKGROUND OF THE INVENTION
Lithium is intercalated into many host materials. These materials include manganese oxides.
Sol-gel processing has become a common method to prepare macromolecular inorganic network materials via hydrolysis and condensation reactions that start from molecular precursors such as organometallic compounds or inorganic salts.
Recent reports have described the increasing worldwide research and development studies of rechargeable lithium (and lithium-ion) batteries that are currently underway.
Idoka, et al.,
Science
276, 1395 (1997) focused attention on tin-based amorphous oxide, while Sato, et al.,
Science
264, 556 (1994) described intercalation into disordered carbons, both of which serve as negative electrodes in lithium-ion cells. The reports have cited the importance of high energy cells for use in portable electronic devices and in electric vehicles. In the latter, the incentive is to lower pollution and the toxic load on the environment.
The positive counter-electrode (cathode) is also of importance, and is usually an intercalation material as well in which the chemical potential of lithium is lower than in pure lithium by several electron volts. Out of the large number of candidate cathode materials, the selection for specific applications is driven by considerations of cost, toxicity, and performance. In addition, the driving range is of major concern for electric vehicles that are powered by rechargeable batteries. Due to their low cost and low toxicity, manganese oxide materials have emerged as important alternatives to the present high energy cathodes based on lithiated cobalt and nickel oxides. This application focuses on synthesis and properties of nanoporous amorphous manganese dioxide, and its various modifications, as a reversible intercalation host for lithium. The amorphous materials of this invention do not suffer from the irreversible phase changes that are characteristic of the crystalline hosts and which limit their performance. The intercalation capacity and specific energy of the amorphous material exceed that of any crystalline manganese oxide, reported either as spinels, see Thackeray, M. M., David W. I. F., Bruce, P. G., and Goodenough, J. B.,
Materials Res. Bull
. 18 451-472 (1983); Tarascon, J. M., Guyomard, D.,
Electrochimica Acta
38, 1221-1231 (1993); Pistoia, G., and Wang, G.,
Solid State Ionics
66, 135-142 (1993), or as layered materials by Armstrong, A. R., and Bruce, P. G.,
Nature
381, 499 (1996). Another amorphous material, manganese oxyiodide, has been reported very recently by Kim, J., and Manthiram, A.,
Nature
390, 265 (1997), and comparisons with the present material will be discussed further below.
Manganese oxides are among the most attractive cathode candidates for lithium batteries. Among the advantages they offer are low cost and relative non-toxicity, in addition to superior electrochemical properties such as high voltages. The most extensively studied form of manganese oxide cathodes is LiMn
2
O
4
of spinel structure. Up to ca. 0.5 moles of lithium per mole of Mn can be intercalated reversibly into this cathode either in the 4 V region (x=0 to 1, Li
x
Mn
2
O
4
) or in the 3 V region (x=1 to 2, Li
x
Mn
2
O
4
). Recently another form of lithium manganese oxide, LiMnO
2
of layered structure, was reported by Armstrong, A. R. et al,
Nature
381, 499 (1996). Up to ca. 1 mole of lithium per mole manganese can be electrochemically extracted out of this material during first charge (x=1 to 0, Li
x
MnO
2
); however, the charge/discharge capacity of subsequent cycles is less than 50% of that of the first cycle. It has been subsequently reported that lithium extraction and reinsertion into this material is not a reversible intercalation reaction and that the material is converted from the layered structure to the spinel structure upon cycling, see Vitins, G.; West, K.;
J. Electrochem Soc
., 144,2587 (1997).
Various methods for preparation of amorphous manganese oxides are known. For example U.S. Pat. No. 5,674,644 assigned to General Motors Corporation is directed to a “Manganese Oxide Electrode and Method”, which is specifically directed to a lithium ion cell.
Since this invention and the GM patent are both concerned with nominally “amorphous Manganese Oxide” a comparison of the GM patent and this invention seems warranted. The important differences between the two are:
1. Although the materials covered by the GM patent (hereafter referred to as the GM materials) and the materials of this invention might both be referred to as “amorphous manganese oxide”, they are very different materials with different chemical compositions and for different uses.
2. The chemical compositions of the materials of this invention are different from those of the GM materials. The GM materials contain a large amount of lithium or sodium, which is evident from
FIG. 6
of the patent. The FIGURE, which is characteristic charge-discharge curves of the GM materials, shows the materials are charged first. That means they contain a large amount of lithium (or possibly sodium) and they are for use as the positive electrode for lithium ion batteries, as claimed throughout the patent. The materials of this invention contain no lithium and only a tiny amount of sodium.
3. The materials of this invention possess much higher charge capacity (milliampere-hour per gram (mAh/g) than the GM materials. The highest capacity among the GM materials is about 240 mAh/g, while the highest capacity of the materials of this invention is 436 mAh/g.
4. The most preferred among the GM materials, including the one that gives the highest capacity, contain electronically conducting polymers, such as polyaniline, mixed with manganese oxide, while the materials of this invention contain no conducting polymers whatsoever.
5. The method for synthesizing the materials of this invention is very different from the method for synthesizing the GM materials as described in the patent, although they can both be referred to as a “sol-gel method.” “Sol-gel synthesis (or method)” is very broad and entails different ways of synthesis (like the term “solution synthesis”). Specifically, the GM method involves mixing a solution containing manganese of high valence with a solution containing manganese of low valence, while the method of this invention involves mixing a solution containing manganese of high valence with a solution containing an organic reducing agent (no manganese). Further, the synthesis for this invention involves treatment with an acid such as sulfuric acid to induce a disproportionation reaction, while the GM method involves no such treatment. Still further, the method of this invention involves ultra sonication, while the GM method does not. There are still other differences between the two methods, which need not be described here.
6. In synthesizing the materials of this invention, the synthesis solutions are not heated at all. The entire synthesis process is carried out at room temperature. The synthesized materials in some cases may be heated to around 100° C. before use. In the GM method, the synthesis solution is heated to 80° C. for the synthesis process and the synthesized material is heated to 180° C. before use.
7. The fact that the materials of this invention have different chemical compositions, much higher charge capacities, and are synthesized by a different method (and also most likely have a different crystal nano- and micro-structure), among other different factors, substantiate the difference between the materials of this invention and those of the GM patent.
8. The terms “amorphous manganese oxide (or dioxide)” and “sol-gel method” are generic terms which do not describe specific technical content. There can be many different kinds of materials under the generic term “amorphous manganese oxide (or dioxide)” with different local atomic arrangements and chemical compositions (not all amorphous structures are the same. They are all referred to as “amorphous” only in that X-ray powder diffraction cannot tell a diff
Owens Boone B.
Smyrl William H.
Xu Jun
Regents of the University of Minnesota
Vidas, Arrett & Steinkraus PA
Weiner Laura
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