Sol-gel compositions and polymeric ion conductive film...

Details Sol-gel compositions and polymeric ion conductive film... Sol-gel compositions and polymeric ion conductive film...

1998-08-11

2001-01-09

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S104000, C524S113000, C524S205000, C524S233000, C524S378000, C524S280000, C525S104000, C525S105000

Reexamination Certificate

active

06172152

ABSTRACT:

TECHNICAL FIELD
The present invention relates to sol-gel composition, polymeric ion conductive films prepared therefrom and a method for preparing the same. Specifically, this invention relates to ion conductive sol-gel composition which is easy to process and from which an ion conductive film can be easily prepared, and provides a polymeric ion conductive film having an excellent mechanical strength and high lithium ion conductivity at room temperature and a method for preparing the same. More specifically, this invention is intended to provide ion conductive sol-gel composition comprising a polyalkylene glycol-substituted trialkoxysilane (PAGTAS) such as polyethylene glycol-substituted trialkoxysilane (PEGTAS), a tetraalkoxysilane (TAOS) such as tetraethoxysilane (TEOS) and an alkaline metal salts such as lithium salt as major components, and a polymeric ion conductive film having an excellent mechanical property, strong adhesiveness, and high ion conductivity at room temperature, and a method for preparing the same by processing the ion conductive sol-gel compositions. Preferably, the ion conductive sol-gel composition of this invention comprises a polyalkylene glycol-substituted trialkoxysilane (PAGTAS), a tetraalkoxysilane (TAOS) and an alkaline metal salt.
Ccmpared with conventional electrochemical devices using liquid electrolytes, electrochemical devices using solid electrolytes are advantageous in that they avoid solution leaking problems, can be prepared in thin-film form, and can be used in portable electronics or automobiles due to their small size. Particularly, solid polymeric electrolyte thin films have been the focus of concentrated research and development efforts because they can provide chemical cells with high charging-discharging efficiency; cells made from them can adapt various shapes and are light-weight.
For preparing solid chemical cells having such advantages, a method for using polymeric compounds as electrolytes is recently being developed. This is because polymers can be processed into thin films, can dissolve salts and have ion permeability and thus polymers can be used as electrolytes. Solid electrolytes also are advantageous in that they have low cell resistance and high electrical current under low electric current density.
As described above, such polymeric electrolyte thin films (ion conductive thin films) used in solid chemical cells should have good ion conductivity and mechanical property; however, it is difficult to improve both of these properties just by altering physical properties such as molecular weight of the polymer matrix or glass transition temperature. Therefore, it is required to develop new polymeric electrolytes which have both improved ion conductivity and mechanical property.
Bauer et al., in U.S. patent application Ser. No. 4,654,279, disclosed a cell using a two continuous phase network of conductive liquid polymers of a continuous network of a cross-linked polymers to improve mechanical properties of solid electrolytes and of an ion conductive phase which provides pathways for delivering ions through a matrix of the mechanical supporting phase.
Le Mehaute et al., in U.S. patent application Ser. No. 4,556,614, disclosed solid electrolytes for electrochemical devices containing at least one type of complex forming polymers and at least one type of ionizable alkali salts complexed with said polymers, and a method for producing such solid electrolytes in which said complex forming polymers are mixed in amorphous form during the process of cross-linking.
Xia et al. disclosed polymeric electrolytes prepared by polymerizing oligo-oximethylmethaacrylate (Solid State Ionics, 1984, 14, 221~224).
However, polymeric electrolytes prepared in the above-mentioned inventions have problems when actually applied to electrochemical devices; for example, the ion conductivity of the polymeric thin films so prepared varies greatly with temperature and the ion conductivity at room temperature varies with time because it was difficult to prepare a completely non-crystalline (amorphous) thin film. Moreover, such polymeric thin films were difficult to be applied to batteries or solid electrochemical devices in that, ion conduction occurs by the chain movement of polyoxyethlyene units substituted as side-chains to the polymer back bone. Such chain movement of polyoxyethylene side chains is generally slow and thus ion conduction in these polymeric films is inefficient.
Therefore, polymeric electrolytes prepared by such methods have low ion conductivity (less than 1×10
−5
S/cm). Furthermore, poor adhesiveness of these electrolyte films for electrodes causes problems such as the cracking of the electrolytic film, reducing the cycle life of electrochemical devices.
To solve these problems, polysiloxane derivatives having a more flexible chain structure and low glass transition temperature have been under development. Smid et al. and Fish et al. disclosed their findings where crystallization of polyethylene glycol (PEG) is prevented and ion conductivity at room temperature is improved by attaching low molecular weight polyethyleneglycol (PEG) units to a side-chain of poly(hydrogen methylsiloxane) (J. Smid, D. Fish, I. M. Khan, E. Wu, G. Zhou, Silicon-based Polymer Science: A Comprehensive Resource, 113-123; Daryle Fish, Ishrat M. Khan, Johannes Smid,
Makromol. Chem., Rapid Commun
., 7, (1986) 115-120). However, in this case, the polymers have been cross-linked to maintain mechanical strength, but the cross-linked polymers have lower ion conductivity.
Moreover, Bouridah et al. disclosed polyurethane-derived polymers based on polydimethylsiloxane-PEO (A. Bouridah, F. Dalard, D. Deroo,
Solid State Ionics
. 15, (1985) 233), but it is difficult to actually use them in electrochemical devices because the unreacted residual isocyanate group lowers electrochemical stability.
SUMMARY OF THE INVENTION
To solve these problems, the inventors of the present invention researched on polymers having rubber elasticity and ion conductivity and, in particular, they focused on siloxane polymer matrix containing a polyoxyethylene block to give ion conductivity. As a result, the inventors found that homogenous composition can be prepared by adding a polyethyleneglycol substituted trialkoxysilane, namely a sol-gel precursor into a sol-gel mixture; an ion conductive polymeric thin film prepared therefrom shows excellent mechanical property.
More specifically, the inventors found that a sol-gel precursor substituted with polyalkyleneoxy units can be dissolved in conventional organic solvents and developed a method for preparing a polymeric ion conductive film having an excellent mechanical property, from compositions containing such sol-gel precursor, tetraalkoxysilane (TAOS) and polyalkyleneoxyglycol or/and its ether, and electrolytic salts such as lithium salts. It was found that the conductivity at room temperature of the ion conductive film so produced has improved to be higher than 10
−4
S/cm and solid electrolyte film with excellent adhesiveness can be formed when an appropriate amount of electrolytic salts is mixed. Such polymeric ion conductive film can be separated as free standing film after preparation, is electrochemically stable, has excellent adhesiveness in case of readhesion, and can be used in lithium ion cells and solid electrochemical devices.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a sol-gel composition containing 1~90% by weight of a polyalkyleneglycol-substituted trialkoxysilane of Formula 1, 10~95% by weight of tetraalkoxysilane (TAOS), hydrochloric acid, organic solvent, and a 1~90% by weight of a polyalkyleneglycol of Formula 2 and/or an alkyl ether thereof, and optionally 1~70% by weight of a lithium salt of Formula 3. Such sol-gel composition can be prepared with high viscosity when concentrated by 10~90% relative to its weight before or after adding the lithium salts.
[Formula 1]
[Formula 2]
R
2
—O—(CR
3
2
—CR
3
2
—O)
z
—R
2
[Formula 3]
A
+
B
−
In

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