Patent Application
20120058392
Rechargeable batteries with aluminium anode, plasma electrochemistry of aluminium vapour
Environment concerns on fossil fuels which increase the carbon oxide concentration in the atmosphere, economic concerns on the increasing costs of exploring fossil fuels, political concerns on the social stability of the countries where the fossil fuels are located, stimulated research on alternative sources of energy. The most convenient way to transport energy is by converting primary renewable energy sources into electricity, which can be easily transported by metal cables.
The supply of electric energy for transports like cars and trucks has the difficulty of finding a device which is cheap, and presents a sufficiently large capacity per unit of weight for storage of electricity.
The Argonne laboratories filed several patents on batteries using an aluminium anode and an aqueous electrolyte. They present a big storage capacity per unit weight, they are inexpensive and they are in use for transportations in cars of the US Army.
However, these batteries are not rechargeable.
The difficulty to make aluminium anode batteries rechargeable is the fact that aluminium appears almost exclusively as an ion with 3 positive charges, which corresponds to an ionisation energy of about 60 eV. In aqueous electrolytes, the bond Al—O is almost covalent, and needs a lot of energy to be broken. This is the reason why the aluminium production from the ore bauxite (aluminium oxide), is so energy consuming.
We tried to use non aqueous electrolytes, like ionic liquids, tetrafluorborates, hexafluorphosphates, Bis (trifluoromethylsulfono)imide but always came to an unstable quickly falling tension discharge curves, caused by side reactions of aluminium ions with the electrolytes and changes in the surface of the aluminium electrode.
We looked into literature on plasma electrochemistry, but did not find any application to aluminium batteries. Aluminium vapour in plasma state would avoid any problems with undesirable side reactions of aluminium with the electrolyte.
We are now proposing an electrolyte composed of ionized aluminium vapour. We consider following physical properties for aluminium:
Melting point 660° C.
Boiling point 2467° C.
Vaporization enthalpy 293.7 kJ/mole
Ionization enthalpy 6200 kJ/mole=62 eV
Vapour pressure at 1217° C.=1.33 pascal
The container for the electrolytic cell is quartz, which has a melting point of 1710° C.
The anode is graphite, which has a melting point of 3550° C.
The cell itself is a cylinder with round bottoms for supporting pressure with the axis in a vertical position. This cell is heated by microwaves created by an external coil.
The aluminium electrode is down and connected by a wire to the exterior circuit.
The graphite electrode is in the top, connected by a wire to the exterior.
A quartz pipe with 5 mm diameter and a valve is welded to the middle of the quartz cylinder and is used to make a vacuum of 10-6 pascal before heating.
After reaching a temperature of about 1000° C. we applied a voltage of 10 Volt in order to load the cell by transferring aluminium atoms from the aluminium electrode to the plasma and from the plasma the aluminium ions are transferred to the graphite electrode.
After one hour loading, we stopped. Then we could measure a voltage of 5.6 Volt, stable during one hour. Further work is in progression.
We built a quartz cylindric ampoule with round tops with 30 mm diameter, 60 mm length, 5 mm thickness. Before welding on of the tops, we introduced in the bottom 5 g of aluminium granules connected to the outside with a tungsten wire with 2 mm diameter.
In the top of the ampoule with built a porous graphite electrode with 10 mm diameter and 10 mm length connected also by, a tungsten wire with 2 mm diameter to the outside of the ampoule.
We welded the upper top and made vacuum of 1 pascal.
We introduced the ampoule in a microwave furnace and heated up to 1200° C.
We applied an exterior continuous tension of . 10 volt during one hour. Then we stopped and measured the discharge tension during one hour. It was quite constant at 5.6 Volt.
