Patent Application
20050220699
The present invention is in the field of production of Chevrel phase materials. The product of the method of the invention may be used in the manufacturing of superconductors, catalysts and cathodes for electrochemical cells. 10
Chevrel compounds, also known as Chevrel phase compounds or materials, typically consist of molybdenum and a chalcogen such as sulfur, in a specific stoichiometric ratio. Chevrel phase materials are proposed as starting material for the production of superconductive components, catalysts for the petroleum industry and cathodes for batteries.
Chevrel compounds may contain other metals in addition to molybdenum. The incorporation of the additional metals into the Chevrel compound can be performed either in a chemical or electrochemical reaction. Energy is released upon the inclusion of such additional metals in the Chevrel crystal, and the inclusion is reversible at least to some extent. This property provide the grounds for the use of Chevrel materials as cathodes in electrochemical cells.
A method for the preparation of Chevrel compounds according to the present invention uses a low melting salt as a flux. In prior art methods, Chevrel materials are prepared by mixing of chalcogens, molybdenum and an additional leachable metal, such as copper. The ingredients are mixed and heated under a vacuum. Later, the vacuum is stopped and the leachable metal is leached. In the method of the invention, a flux in the form of low salt is added, obviating the vacuum and decreasing the temperature of production.
The present invention provides a method for the production of Chevrel phase materials consisting of molybdenum reacted with a chalcogen, and in some cases, also with an additional metal, called ternary metal. The overall process in which the invention is incorporated is described schematically with reference to
In the laboratory, on a small scale of a few grams to a few tens of grams a Chevrel phase material (CPM), is produced as in the prior art, as will be described next with reference to
The product of the reaction is Cu2Mo6S8 (Chevrel phase material). At step 68 the material is completed and can be collected for further processing, for example, for the production of cathodes for electrochemical cells.
Industrially, the procedure preferably employs different starting materials. Such a process utilizes mainly salts and compounds of molybdenum, the chalcogenide and the ternary metal, in case it is incorporated. As an example, 0.4 g of CuS, 1.0 g of MoS2, 0.6 g of Mo and 2 g of KCl (as a flux) are mixed. The ratios given reflect the calculation relating to the equation as follows:
2CuS+3MoS2+3Mo Cu2Mo6S8.
The KCl is used conveniently but can be replaced by any low melting point1salt used as a flux but not reactive otherwise. The obtained mixture is placed in alumina crucible in an open vertical furnace under inert gas flow. The reaction mixture is heated to the 850° C. for 60 hours, after which it is cooled to room temperature. Then, the reaction products are washed by water for removing the salt flux. The obtained powder is filtered and washed four times with distilled water. After washing sample is dried at 110° C. and prepared for XRD (X-ray diffraction) analysis. The procedure can be modified as to include other metals instead of copper solely or in combination, typically in the form of sulfides. For example ZnS, NiS, Ag, Pg, Mg and Li. Generally, the stoichiometric formula of the generalized Chevrel phase material is as follows:
MxMo6S8
Where: M stands for metal, x stand for 1 to 4.
Sulfur can be replaced partially or completely by selenium. Suitable sources for selenium in this case are metal selenides such as MoSe2, CuSe, CuSe2, NiSe, ZnSe. The product produced using such starting materials has a formula as follows:
MxMo6S6—ySey
Where x=1 to 4, M standing for any metal, and y=0 to 6.
Then, the additional metal, when present, is leached out of the Cu2Mo6S8 (Chevrel phase). The purpose of the leaching is to obtain an empty structure of Mo6S8, For example when the product is used for the manufacturing of cathodes. Two leaching regimes can be employed. An aqueous phase leaching is performed as follows: 15
A non-aqueous phase leaching is performed as follows:
In order to improve the kinetic properties of the leached CPM it is desirable to decrease the particle size of the product. An optional milling process for such is described next. The milling should be performed under inert atmosphere such as pure argon using, for example, a Crescent-Wig L-Bug Amalgamator (Model 3110B).
Quality assessment of the composition of the invention employs two procedures performed serially.
In one procedure, XRD measurements are performed in order to verify that the diffraction pattern obtained from this material is indeed of pure Mo6S8 (Chevrel phase material). The XRD patterns of Cu2Mo6S8 and Mo6S8 are described in
In the other procedure, electrochemical measurements are used to determine the quality of the product. Electrodes are prepared by applying 5-15 mg/cm2 on stainless steel mesh (200 mesh) from slurry of 80% cathode material, 10% carbon black and 10% PVdF (Aldrich). This slurry is prepared with addition of N-methyl-pyrolidon (NMP). The traces of NMP are removed from the electrodes by drying at 800 C for 20-30 minutes. The conditions for the electrochemical measurements are: galvanostatic cycling (5-10 cycles) at current density of 0.1 mA/cm2. On the first discharge a theoretical specific capacity of 120-130 mAh/gr is expected. From the second discharge, the expected specific capacity is not less than 85 mAh/gr and the reversibility should be close to 100%.
| Number | Date | Country | |
|---|---|---|---|
| 60558626 | Apr 2004 | US |
