Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-12-22
2001-11-13
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231950, C029S623500
Reexamination Certificate
active
06316143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an electrode for a rechargeable lithium-ion battery and to a method of fabrication thereof.
2. Description of the Prior Art
Lithium-ion batteries traditionally use lithium metal oxides (LiMO
2
where M=Co or Ni) as cathodes and carbon anodes. The batteries are so named because lithium ions are shuttled back and forth on charge and discharge between the anode and the cathode. On charge, the ions are electrochemically extracted or deintercalated from the lithium metal oxide cathode and inserted or intercalated in the carbon anode. On discharge, the lithium ions are deintercalated from the carbon anode and intercalated into the cathode.
Of all the carbon anode materials that can be used, graphite provides the most capacity, intercalating one lithium per six carbon atoms to form the phase LiC
6
. More recently, it has been shown that the graphite can be replaced by materials such as SnO or SnO
2
which have almost twice the gravimetric capacity as graphite. The materials are reduced at the anode to form first Sn and lithium oxide. For example, for SnO, the reaction may be written as:
2Li
+
+SnO+2e−→Sn+Li
2
O (1)
This reaction is irreversible, and results in considerable capacity loss on the first cycle due to the formation of Li
2
O. Upon further charging of the cell, the tin alloys with lithium. Several intermetallic lithium-tin phases are formed. Finally, the phase Li
4.4
Sn, the phase of highest lithium content, is formed as follows:
4.4Li
+
+Sn+4.4e
−
→Li
4.4
Sn (2)
Since the alloying of tin is reversible, the battery can then cycle reversibly provided that fracturing of the alloyed tin particles does not cause the active material from losing electrical contact with the anode substrate and irreversible capacity loss. This type of capacity loss is a recurrent problem with this type of electrode. The problem may be overcome only by using materials of extremely small particle size that are separated by an electrochemically inert oxide matrix. However, up to the present, techniques for developing such materials of extremely small particle size have not been provided for ductile materials such as tin.
Furthermore, according to the previous state of the art, processes for development of lithium ion batteries or cells begin with SnO as the active anode material in the lithium-ion cell. Charge from the cathode is required to reduce the SnO to Sn. In order to do this, extra cathode material has had to be added to the cell, and the resultant battery has been large, heavy and of unsatisfactory efficiency.
SUMMARY OF THE INVENTION
The present invention generally relates to electrodes for rechargeable lithium-ion batteries, and to a method of fabricating same. More particularly, the method of the invention comprises a novel method of preparing negative electrodes for rechargeable lithium-ion batteries, which method results in more efficient, lighter or smaller chargeable lithium-ion batteries than batteries having metal oxide anodes of the type MO or MO
2
, where M=Sn, Pb, Ge, Si, Ag and similar metals, as well as glasses formed from these oxide materials. The method of the invention replaces the metal oxide with a mixture of the metal and Li
2
O. The method is applicable to many metal oxides, but the application of the method to SnO, as well as to SnO
2
and tin oxide glasses, is the preferable application of the method.
The method of the present invention, which involves reacting the SnO with lithium nitride (Li
3
N), eliminates the irreversible capacity loss associated with the process of equation (1) above because the electrochemical reaction of equation (1) is replaced by a chemical reaction that takes place during the milling process, in accordance with the following:
2Li
3
N+3SnO→3Sn+→3Li
2
O+N
2
↑ (3)
As a result of the present invention, a lighter, smaller and more efficient power source is provided. Moreover, the invention provides a process for producing tin of a smaller particle size in an Li
2
O matrix, than can be achieved by simply mixing Li
2
O and Sn, and grinding them together. Whereas larger particle size materials yield more readily to cracking, mechanical degradation, and electrical isolation of active material as cycling continues, the smaller particle size material provided in accordance with the present invention is less prone to such stresses, and provides a longer life cycle for the lithium-ion battery.
Therefore, it is a primary object of the present invention to provide a rechargeable lithium-ion battery.
It is an additional object of the present invention to provide a method for fabricating a rechargeable lithium-ion battery.
It is an additional object of the present invention to provide a method which results in the development and use of extremely small particle size materials.
It is an additional object of the present invention to provide a rechargeable lithium-ion battery which is smaller in size, lighter, and more efficient than batteries of the prior art.
The above and other objects, and the nature of the invention, will be more clearly understood by reference to the following detailed description, the associated drawings, and the appended claims.
REFERENCES:
patent: 5677083 (1997-10-01), Tomiyama
patent: 5707756 (1998-01-01), Inoue et al.
patent: 5928812 (1999-07-01), Xue
patent: 5965293 (1999-10-01), Idota et al.
Behl Wishvender K.
Foster Donald L.
Read Jeffrey
Wolfenstine Jeffrey
Adams William V.
Alejandro Ray
Biffoni U. John
Clohan, Jr. Paul
Kalafut Stephen
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