Patent Application
20240194864
This invention relates to safe rechargeable magnesium-sulfur batteries, having high energy density and long cycle life.
It has been recognized that there is a need for low cost, safe and higher energy density batteries than present electric vehicle batteries. Elimination of the “range anxiety” in the use of electric vehicle, as well as reducing the weight, flammability and cost of the batteries are critical goals. The same requirements are for batteries in military applications. The desired range of electric vehicles should be 600 miles per one charge, approximately double of today's best electric vehicle range with 250 Wh/kg batteries. Therefore, the desired energy density of electric vehicle batteries is approximately 500 Wh/kg or more.
It is known in the art, that one promising battery chemistry to achieve this goal, is magnesium sulfur chemistry, which has high theoretical energy density, due to −2.38V potential of magnesium, and having two valences. Magnesium also has higher specific capacity 2.2 Ah/g (versus graphite 0.340 Ah/g) and 3.8 Ah/cm3 volumetric capacity, (versus lithium 2.06 Ah/cm3).
Sulfur has one of the highest specific capacities 1.6 Ah/g, as cathode material. Both, magnesium and sulfur are plentiful and low cost. However, magnesium sulfur chemistry has a problem in finding a compatible electrolyte with both electrodes, and suffers from sulfur dissolution into electrolytes. Some progress has been made, as can be seen in the U.S. Pat. No. 8,354,193, B2 of John Muldoon et al., but the cycle life is still short, and the cells suffer with a rapid decline in capacity. Sulfur can be now stabilized by carbon nanotubes.
Instant invention overcomes these problems and provides safe, magnesium sulfide/sulfur batteries with high energy density of approximately 500 Wh/kg, and good cycle life at low cost.
It has now been found, that a rechargeable non-flammable, high energy density battery can be made by using magnesium (Mg) metal foil or plate, or a porous carbon as anode, and magnesium sulfide (MgS) stabilized by carbon nanotubes, or just MgS with carbon nanotubes as cathode, encased in a porous carbon structure carrier. If carbon anode is used, such battery is referred to as magnesium-ion battery.
Electrolyte in such battery is preferably non-aqueous, aprotic, sulfolane based solvent, mixed with DME and or THF, containing magnesium triflate salt or other —Mg salts, like MgPF6, which electrolyte is soaked into the cathode and into a porous electrically insulating separator between the anode and cathode, and is in contact with the magnesium or carbon anode. The electrolyte may optionally also contain a small amount of MgS and S mixtures.
Other electrolytes, such as sulfolane mixed with sulfone and a magnesium based salt, and other electrolytes may be useable with the above electrodes, but it is important to note, that the stabilized magnesium sulfide (MgS) cathode will not dissolve in electrolytes, and thus makes) the high cycles life battery possible.
The cell(s) of this battery is (are) then enclosed in a moisture proof enclosure with electrical terminals exiting from the enclosure in a sealed manner. The terminals are electrically connected to the anode and cathode electrodes, and may be preferably made from nickel foil or microgrid.
The porous separator may be preferably made from polytetrafluoroethylene (Gore Teflon), or polyethylene (Celgard). The cathode current collector in contact with the carbon carrier may be of aluminum microgrid or foil. Magnesium is also much less sensitive to moisture and is less flammable, due to its higher melting point. The flammability can be also eliminated by alloying magnesium with a low percentage of calcium (Ca) (about 5% by weight).
Only the magnesium is cycled, due to presence of only Mg based salt in the electrolyte. However, the moisture proof enclosure is necessary, due to sensitivity of MgS and Mg-salts to water. This cell can be also discharged to 0 volts without damage, and recharged again. It was also found, that this battery is very safe, since the end of life is MgS by-product, which is very stable. Magnesium also does not create dendrites, which results in high cycle life of the battery and added safety. The cell construction of this battery is preferably prismatic bi-cell, in aluminum pouch enclosure, but it can be also cylindrical, round structure, or flatly wound “prismatic” in metal can enclosures. The magnesium metal foil anode may be also replaced by a metal current collector foil or grid only, like Mg, Al, Cu. Ni, or Li. In these cases, the metal foils or grids serve as current collectors to which a nickel or copper terminal tab is electro-conductively attached. In this case the source of magnesium is MgS in the cathode, and Mg is plated onto the anode metal current collector upon charge, or may be inserted into a carbon anode if carbon is added. It should be noted, that only magnesium is cycled between the MgS cathode and the anode metal current collector, or the graphite anode. If the metal collector is lightweight aluminum, or lithium, or LiMg, or AlLi alloy, it additionally increases the energy density of the battery. The magnesium only is cycled between the electrodes, because the electrolyte contains only Mg salts. This provides for long cycle life, high capacity and safety. Lithium or magnesium, or aluminum current collector is preferred, but any lightweight and electrically conductive metal compatible with electrolyte for sulfur can be also used. Magnesium and sulfur are also plentiful and low cost. This battery contains no toxic and expensive heavy metal oxides like cobalt and nickel oxides, and thus is environmentally friendly. Due to low 2 V voltage cells, even expensive and heavy copper collectors can be avoided.
Low cost MgS can be synthesized from MgO+C+S. The MgO is plentiful and cheap, since it is used in fire resistant sheetrock panels.
The liquid electrolyte provides for high rate of charge and discharge.
The principal object of the invention is to provide a rechargeable battery that has a higher energy density than present electric vehicle batteries.
A further object of the invention is to provide a rechargeable battery, which is safe and non-flammable and environmentally friendly.
A further object of the invention is to provide a rechargeable battery, which has a high rate of discharge and charge, and has long cycle life.
A further object of the invention is to provide a rechargeable battery, which is at low cost and is suitable for mass production.
Other objects and advantageous features will be apparent from the description and claims.
The nature and characteristic features of the invention will be more readily understood from the following description taken in connection with the accompanying drawing forming part thereof in which:
It should, of course be understood that the description and drawings herein are merely illustrative, and that various modifications and changes can be made in the structures disclosed without departing from the spirit of the invention.
When referring to the preferred embodiments, certain terminology will be utilized for the sake of clarity. Use of such terminology is intended to encompass not only the described embodiments, but also technical equivalents, which operate and function in substantially the same way to bring about the same result.
Referring now to the drawings
Preparation of the stabilized cathode is as follows:
Said prismatic battery may be also made multi-celled, with the cells connected in parallel and sealed in a similar enclosure with terminals.
It will thus be seen that safe, high energy density batteries with long cycle life are herein described, with which the objects of the invention are achieved.
| Number | Date | Country | |
|---|---|---|---|
| 63103004 | Jul 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17300475 | Jul 2021 | US |
| Child | 17803825 | US |
