Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1995-06-07
2002-05-21
Everhart, Caridad (Department: 2825)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S218200, C029S623100
Reexamination Certificate
active
06391492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a secondary battery which can repeatedly be used. More particularly, this invention relates to a reliable secondary battery capable of preventing-short circuits due to dendrite growth, even when the battery is repeatedly charged and discharged.
2. Related Background Art
Since global warming is expected due to the greenhouse effect caused by an increase in CO
2
and so forth, the construction of thermal power plants has become problematic. Accordingly, it has been considered feasible to perform so-called load levelling for the purpose of effectively using generators by accumulating electric power at night in secondary batteries at homes to level the load.
Another desire has arisen to develop a secondary battery which exhibits a high energy density for use in an electric car that does not exhaust air contamination substances. Further, development of a high performance secondary battery has been needed for use as a power source for portable equipment, such as book-type personal computers, word processors, video cameras and portable telephones.
A locking chair type lithium ion battery capable of serving as the foregoing high performance secondary battery and comprising a positive pole activating material comprising lithium ions introduced into an interlayer compound thereof and a negative pole activating material comprising carbon has been developed and partially put into practical use.
However the lithium ion battery has not achieved the high energy density that is the original characteristic of the lithium battery which uses the metal lithium as the negative pole activating material. The reason why a large capacity lithium accumulator of the type that uses lithium metal as the negative pole has not been put into practical use is that the generation of dendrites of lithium (tree branch-like crystals), which are the main cause of short circuiting, cannot be prevented.
The lithium battery, nickel-zinc battery and the air-zinc battery are problematic in that lithium or zinc is, as described above, deposited on the surface of the negative pole at the time of charge. At this time, the current density is locally raised on the negative pole surface depending upon the surface condition, causing lithium or zinc to be selectively deposited in the foregoing place. The deposited metal grows (dendrites) in the form of tree branches upon charging and discharging, while penetrating the separator until it reaches the positive pole, causing a short circuit.
The dendrite reaction mechanism is considered as follows. Since lithium or zinc that deposits at the time of charge has a considerable reactivity, it reacts with electrolytic solution or water or the like in the electrolytic solution, causing an insulating film to be formed which has a large resistance. Therefore, the current density in the foregoing portion is raised at the time of the next charge, resulting in easy dendrite growth. It leads to a short circuit between the negative pole and the positive pole, resulting in that charging cannot be performed.
If the short circuit is extensive, the energy of the battery will be consumed in a very short time, causing the generation of heat. As a result, the solvent of the electrolytic solution can be decomposed, resulting in the generation of gas. When gas is generated, the internal pressure is raised. In the worst, an accidental exposure or fire can be generated. Therefore, there has been a desire for a long life lithium accumulator that does not easily cause internal short circuit even if the charge and discharge cycles are repeated.
Also nickel-zinc batteries and air-zinc batteries generate dendrites of zinc due to repetition of charging and discharging, with the dendrites penetrating the separator. As a result, the zinc negative pole and the positive pole exhibit a short circuit. Therefore, the foregoing conventional technology suffers from an excessively short cycle life.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a lithium, lithium alloy, zinc or zinc alloy secondary battery capable of overcoming the foregoing problems associated with the conventional secondary batteries and exhibiting a long cycle life.
In order to overcome the foregoing problems of the conventional technology, the inventors of the present invention have made energetic studies. As a result, it was found that generation of dendrites of lithium or zinc can be prevented by forming a film permitting ions relating to battery reactions to pass through on the surface of the negative pole.
The present invention is characterized in that a secondary battery comprises a negative pole made of a negative pole activating material, a separator, a positive pole made of a positive pole activating material, an electrolyte (electrolytic solution), a collecting electrode and a battery case, wherein the surface of the negative pole is covered with a film permitting ions relating to battery reactions to pass through.
The material of the film has a molecular structure or small apertures which do not permit the negative pole activating material which precipitates on the negative pole, but which permit ions relating to the battery reactions, to pass through.
The present invention is characterized in that the foregoing material of the film has been electron donative elements or groups for enabling the ions relating to the battery reactions to be easily conducted in the film.
The electron donative element is exemplified by oxygen atoms, nitrogen atoms, sulfur atoms and transition metal atoms, respectively, having a paired electron, a non-paired electron or electron d (electrons in the d quantum shell). The electron donative group is exemplified by a ring compound and a compound having a carbon double bond having electron &pgr; (&pgr; electron resonance) or an aromatic ring.
The film formed on the surface of the negative pole according to the present invention is characterized in that it cannot be dissolved by the electrolyte.
The inventor of the present invention found that treatment of the surface of the negative pole with a nitrogen compound or a halogen compound, which is active in a gas phase, will prevent the generation of lithium dendrites.
According to the present invention, there is provided a secondary battery having a negative pole activating material composed of lithium, a separator, a positive pole activating material, an electrolyte, a collector and a battery case, wherein at least the surface of the lithium negative pole opposing the positive pole is treated with a reactive and gaseous material containing nitrogen or a halogen element.
According to the present invention, there is provided a battery comprising a negative pole, a separator, a positive pole and an electrolyte, wherein one or more layers selected from a group consisting of a conductor layer, a semiconductor layer and an insulating layer are formed between the negative pole and the separator.
If the negative pole activating material is lithium or lithium alloy, the foregoing layer is formed into a micropore structure having small apertures permitting at least lithium ions to pass through. If zinc or zinc alloy is used, the small apertures permit hydride ions to pass through.
The small apertures permitting ions to pass through may be realized by the molecular structure of the material or by a manufacturing method. The small apertures can be easily formed by, for example, injecting an electrolyte into the foregoing layer at the time of forming the layer to manufacture the battery, the electrolyte being eluted to form the micropores. Another method may be employed in which a foaming material is added at the time of forming the foregoing layer, with the micropores being formed by heat treatment or the like.
The structure of the stacked layers may be a single layer or a multi-layer composed of two or more layers or composed of a conductor layer, a semiconductor layer, an insulating layer and a composite layer containing two or more types of elements or compounds.
Kawakami Soichiro
Kobayashi Naoya
Mishina Shinya
LandOfFree
Secondary battery does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Secondary battery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Secondary battery will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2844140