Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-12-14
2001-10-09
Brouillette, Gabrielle (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C029S623500, C029S623300, C429S300000, C429S303000, C429S344000
Reexamination Certificate
active
06299653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel hybrid electrolyte. More particularly, the present invention is concerned with a novel hybrid electrolyte comprising a shaped porous polymer structure comprising a polymer matrix and a plurality of cells dispersed in the polymer matrix, the polymer matrix containing a crosslinked polymer segment and having a specific gel content, wherein the shaped porous polymer structure is impregnated and swelled with an electrolytic liquid. The present invention is also concerned with a method for producing the hybrid electrolyte and a method for producing an electrochemical device comprising the hybrid electrolyte.
The hybrid electrolyte of the present invention has a high ionic conductivity, an excellent stability under high temperature conditions and an excellent adherability to an electrode, so that the hybrid electrolyte of the present invention can be advantageously used as an electrolyte for various electrochemical devices, such as primary and secondary batteries (e.g., a lithium battery), a photoelectrochemical device and an electrochemical sensor. Further, by the method of the present invention, the hybrid electrolyte having the above-mentioned excellent properties and an electrochemical device comprising the same can be surely and effectively produced.
2. Prior Art
Recently, for reducing the size and weight of portable equipments, such as pocket telephones and personal computers, there has been a demand for a battery having high energy density. As a battery for meeting such a demand, lithium ion batteries have been developed. This type of battery has a structure in which a porous separator is disposed between the positive and negative electrodes, wherein the porous separator is not swelled with an electrolytic liquid. For preventing a leakage of the electrolytic liquid used for impregnating the separator, the commercially produced battery of this type has a battery structure wholly packaged in a very strong metallic casing having a large thickness.
On the other hand, so-called solid type batteries produced using a solid electrolyte functioning not only as an electrolyte but also as a separator are advantageously free from the danger of leakage of an electrolytic liquid. Therefore, it is expected that not only is a solid electrolyte useful for providing a battery having improved reliability and safety, but is also advantageous in that both the lamination of a solid electrolyte onto electrodes and the packaging of the resultant laminate to form a battery can be easily performed, wherein the thickness and weight of the battery can be reduced. Especially, a polymeric solid electrolyte comprising an ion-conductive polymer has excellent flexibility for processing and, therefore, not only can a laminate structure composed of the polymeric solid electrolyte and electrodes be easily produced, but also the polymeric solid electrolyte is capable of changing its morphology at an interface between the electrolyte and the electrodes in accordance with the volumetric change of the electrodes caused by the occlusion and release of ions by the electrodes, enabling the interface of the polymeric solid electrolyte to intimately fit over the electrodes without suffering delamination from the electrodes.
As such a polymeric solid electrolyte, an alkali metal salt complex of polyethylene oxide was proposed by Wright in British Polymer Journal, vol.7, p.319 (1975). Since then, researches on various skeletal materials for polymeric solid electrolytes have been energetically conducted. Examples of such skeletal materials include polyethers, such as polyethylene oxide and polypropylene oxide, polyphosphazene and polysiloxane. Generally, polymeric solid electrolytes are provided in the form of solid solutions of a solid electrolyte in a polymeric solid, wherein the solid electrolyte is considered to be uniformly dissolved in the polymeric solid, and are known as dry type polymeric solid electrolytes. However, these polymeric solid electrolytes have a problem in that the ionic conductivity of them is extremely low as compared to that of an electrolytic liquid. Therefore, a battery produced using such a polymeric solid electrolyte has problems in that it has a low charge/discharge current density and has a high resistance.
For solving these problems, various attempts to improve the ionic conductivity of a polymeric solid electrolyte have been proposed, wherein the condition of the solid electrolyte is rendered similar to the condition of the electrolyte in the electrolytic liquid. For example, gelled solid electrolytes are known which are obtained by adding a solvent for the electrolyte (which solvent is capable of dissolving an electrolyte to form an electrolytic liquid) as a plasticizer to a polymer matrix so that the solvent and the polymer matrix together form a gel, wherein the solvent is used for increasing the dissociation of the electrolyte and promoting the molecular movement of the polymer, so that the ionic conductivity of the electrolyte can be increased (see, for example, Japanese Patent Application Laid-Open Specification No. 57-143356). As an example of such a gelled solid electrolyte, U.S. Pat. No. 5,296,318 discloses a gelled solid electrolyte obtained by adding an electrolytic liquid to a vinylidene fluoride polymer so that the electrolytic liquid and the polymer together form a gel. Further, U.S. Pat. No. 5,429,891 discloses a gelled solid electrolyte obtained by adding an electrolytic liquid to a crosslinked vinylidene fluoride polymer to thereby swell the crosslinked polymer so that the electrolytic liquid and the crosslinked polymer together form a gel. In general, when a battery comprising such a gelled solid electrolyte (i.e., a so-called hybrid electrolyte) is produced, a hybrid electrolyte comprising a crosslinked polymer swelled with an electrolytic liquid is produced, and then, a battery is assembled using the swelled hybrid electrolyte, electrodes, etc. With respect to the polymer matrix of such a hybrid electrolyte, a crosslinked polymer can be used. On the other hand, a method for producing a battery comprising a hybrid electrolyte layer is also known, wherein the hybrid electrolyte layer is formed by coating electrodes for the battery with a solution obtained by dissolving a non-crosslinked polymer, an electrolyte and a plasticizer in a low boiling point solvent, followed by removing the solvent by evaporation (see U.S. Pat. No. 5,296,318). Each of these materials is electrochemically stable and has a high ionic conductivity, as compared to that of a conventional dry type solid electrolyte. However, the ionic conductivity of each of the above-mentioned hybrid electrolytes is still unsatisfactory, as compared to that of an electrolytic liquid. Further, a non-porous polymer matrix is used for each of the above-mentioned conventional hybrid electrolytes. Hence, the capacities of the batteries comprising such conventional hybrid electrolytes are disadvantageously low.
As a hybrid electrolyte having a high ionic conductivity, a material has been proposed, which comprises a gel phase (comprising a polymer and an electrolytic liquid) and a liquid phase (comprising an electrolytic liquid), wherein the liquid phase is dispersed in the gel phase. For example, Unexamined Japanese Patent Application Laid-Open Specification No 8-250127 describes the use of a vinylidene fluoride porous polymer sheet as a polymer matrix of a solid electrolyte. In this document, a description is made with respect to a method for impregnating a porous polymer sheet with an electrolytic liquid under high temperature conditions, to thereby form a hybrid electrolyte (comprising the porous polymer sheet impregnated and swelled with the electrolytic liquid), which is similar to the hybrid electrolyte of the present invention. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 6-150939 discloses a method for producing a hybrid (solid) electrolyte, in which a porous structure comprising a crosslink
Hoshi Nobuto
Kuroki Masakatsu
Minakata Takashi
Alejandro Raymond
Asahi Kasei Kabushiki Kaisha
Brouillette Gabrielle
Pennie & Edmonds LLP
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