Gel Polymer Electrolytes
The Pennsylvania State University
posted on 02/05/2009
Gel electrolytes are alternatives to both solid polymer electrolytes (SPEs) and liquid electrolytes for battery applications. The disclosed polymer possess enhanced mechanical stability and an ability, when used in electrolyte systems, to improve the ionic conductivity of the electrolyte systems relative to the ionic conductivity exhibited by SPEs known in the art.
• Gel polymer electrolytes with high mechanical stability
Gel electrolytes are alternatives to both solid polymer electrolytes (SPEs) and liquid electrolytes for battery applications. In organic, liquid-filled batteries, the liquid electrolytes may escape or present a fire hazard and an inert spacer generally is needed to separate the electrodes. Solid polymer electrolyte systems typically possess the mechanical properties and structural integrity required for battery applications, but have inherently lower conductivities due to the more restricted motion of the polymer molecules. Solid polymer electrolytes are non-volatile, non-corrosive materials, which can readily be processed into virtually any shape or size. In addition, the inherent lightness of weight and flexibility of solid polymer systems enable the production of more robust energy storage devices having high energy densities.
Gel polymer electrolyte systems are an attempt to strike a balance between the high conductivity of organic liquid electrolytes and the dimensional stability of solid polymer electrolytes. The design of such gel systems depends on an understanding of the mechanism of ionic conduction in gels, and on the ability to tune the structure of the polymer component in the gel to optimize the overall physical properties. There remains a need for developing still further polymers that possess enhanced mechanical stability and an ability, when used in electrolyte systems, to improve the ionic conductivity of the electrolyte systems relative to the ionic conductivity exhibited by SPEs known in the art.
The gel polymer electrolytes of this invention contain co-substituted linear polyphosphazene polymers and have an ion conductivity at room temperature of at least about 10-5 S/cm. These gel polymer electrolytes comprise: (i) a polyphosphazene having controlled ratios of side chains that promote ionic conductivity and hydrophobic, non-conductive side chains that promote mechanical stability, (ii) a small molecule additive, such as propylene carbonate, that influences the ionic conductivity and physical properties of the gel polymer electrolytes, and (iii) a metal salt, such as lithium trifluoromethanesulfonate, that influences the ionic conductivity of the gel polymer electrolytes.
File Number: 2311
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