Chemistry: electrical current producing apparatus – product – and – Regenerating – salvage or repair feature other than only...
Reexamination Certificate
2000-07-25
2003-02-25
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Regenerating, salvage or repair feature other than only...
Reexamination Certificate
active
06524737
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method to dismantle the sort of batteries with an enclosed cell which is protected by a plastic case. More specifically, it concerns a method to process nonaqueous solvent-type batteries which contain in their electrolytes, salts comprising cations and Lewis acid ions. This method is a safe and efficient way to process used lithium batteries which contain lithium hexafluorophosphate in their electrolytes.
For our purposes a nonaqueous solvent-type battery is a secondary battery which uses a nonaqueous solvent in its electrolytic solution and a light metal such as lithium in its cathode.
A nonaqueous solvent is any solvent other than water. The term is not limited in meaning to simple solvents other than water, but also includes mixtures of solvents.
TECHNICAL BACKGROUND
Recent concerns over the trend toward global warming have resulted in a call for more efficient use of electric power in order to avoid further proliferation of thermal generating plants. One way in which power might be used more efficiently would be to normalize power use by temporarily storing excess power at night and releasing it during the daytime. To bring this about, we must realize secondary batteries capable of storing such power. Concerns over air pollution, too, have led to a call for the development of large secondary batteries which can serve as the power supply for an automobile.
The demand for smaller secondary batteries has also been increasing yearly, both for their usefulness as backup batteries in computers and word processors and for their role as power supplies in small home appliances. In particular, the popularization of portable appliances and the improvement of their capabilities have produced a greater demand for small secondary batteries. With this expanding demand for batteries has come a serious concern that the chemical substances which make up the batteries be used efficiently and that measures be taken to prevent used batteries from posing an environmental hazard.
The sort of batteries now in demand are high-performance secondary batteries with capabilities equal to those of the appliances in which they are used. The most prominent examples of these to have been developed for the market are lithium ion batteries, which use an intercalation complex in which lithium ions have been embedded as the active material of their positive electrode and graphite as the active material of their negative electrode. Lithium, transition metals and other valuable substances which can be reused can be found in the lithium ion batteries. However, these batteries also contain extremely reactive substances like alkaline metals, which are used as the active material for their negative electrode, as well as electrolytes which contain substances likely to react with water.
Thus when we dismantle nonaqueous solvent-type batteries like lithium ion batteries, we must safely deactivate their active substances, including their active materials and their electrolyte solution, and at the same time safely and effectively recover any valuable materials which can be reused.
However, metallic lithium (which reacts with water to produce hydrogen) and organic solvents are used in the construction of lithium ion batteries, and they contain numerous other combustible compounds; so it is extremely difficult to recover valuable materials such as lithium cobalt oxide from these batteries.
In schemes disclosed in Japanese Patent Publications (Kokai) 6-346160 and 7-245126 to recover valuable materials including cobalt (actually, lithium cobalt oxide) from used lithium secondary batteries, the used battery is heated and crushed. The crushed materials are passed through a sieve and then separated by a magnet.
In Japanese Patent Publication 7-207359, the used lithium secondary battery is burned in a primary combustion process at 350 to 1000° C. It is then crushed and the resulting fragments are passed through a sieve and subjected to a secondary combustion process. The fired fragments are treated with an acid, the pH is adjusted to between 4 and 5.5 by an oxidizing gas which is blown into the acid, and the solution is filtered. An alkali is added to the filtrate, and the valuable materials are recovered from the resulting precipitate.
However, lithium ion batteries which are enclosed cells are enclosed in a protective plastic case. Their constituent materials, which include the active material in the negative electrode, the separator, the active material in the positive electrode, the electrolyte solution and the collector, are enclosed in a protective stainless or other type of steel case. If, using one of the techniques discussed above, a used lithium secondary battery of this sort is heated to between 350 and 1000° C. in a primary combustion process, the heat of combustion will cause the lithium cobalt oxide in the enclosed cell to decompose and emit oxygen. At the same time, the volatile (and flammable) solvent in the electrolyte solution will vaporize. The pressure of the vaporization may cause the cell case to burst open, in which case the vaporized and combustible organic solvent and oxygen will ignite. If the solvent and oxygen experience a sudden pressure spike while the case is still intact, they may even explode.
In Japanese Patent Publication 6-251805, a device such as a water jet is used to cut apart or make a hole in the case of a lithium battery. The lithium is processed by reacting it with water or some other reactant. The lithium, the hydrogen which is the other product of the reaction and the electrolyte solution are recovered. There is no combustion to cause a fire, and the materials are recovered safely and efficiently. To minimize combustion with the hydrogen when the battery case is cut open, the process is carried out in an atmosphere of inert gas. However, the use of a water jet requires that it be performed at normal temperatures. If any of the jet is at a lower temperature, and the battery is not fully discharged, the reactive lithium remaining in it will react violently with the moisture component in the air, producing combustible hydrogen gas, as will be discussed shortly.
In Japanese Patent Publication 6-3338352, three processes are used. In Process 1, the negative electrode containing lithium is exposed. In Process 2, the electrolyte is separated from the battery. In Process 3, to prevent a large quantity of hydrogen from being generated when the lithium and water or alcohol come in contact, the surface of the negative electrode which contains the lithium is treated with a solvent such as alcohol or water. Once this is completed, the inside of the negative electrode is also treated with a solvent.
In the prior art techniques described above, the process by which the negative electrode containing lithium is exposed consists of crushing the battery with a hammer crusher, a diamond cutter or a cutter-mixer. When the plastic and metal cases of a number of enclosed cells are cut open simultaneously as described above, the residue of the plastic cases sticks to the crushed fragments of the metal cell cases, and it is very difficult to remove. In addition, when a lithium ion battery which is not fully discharged is crushed, a short circuit will be created when its positive and negative electrodes come in contact with each other. The short circuit will generate Joule heat, causing the temperature inside the battery to rise. The lithium cobalt oxide comprising the positive electrode will decompose, producing oxygen. At the same time, the volatile (and flammable) solvent in the electrolyte solution will vaporize. If a spark is produced when the case is cut, the vaporized combustible organic solvent and the oxygen can ignite; or, if the pressure in the battery spikes abruptly, they can explode.
Another shortcoming of the prior art techniques described above is that a two-step treatment is required to prevent a large quantity of hydrogen from being generated when the lithium and water or alcohol come in contact. In order to execute the two-step process, the composit
Honmura Shiro
Kamimura Takeo
Nishida Kiyonori
Sasaki Kenji
Tanii Tadaaki
Kalafut Stephen
Mitsubishi Heavy Industries Ltd.
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