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Publication Date

Fall 2020

Degree Type

Thesis - Campus Access Only

Degree Name

Master of Science (MS)


Mechanical Engineering


Sang-Joon Lee

Subject Areas

Mechanical engineering


Composite electrolytes have potential to achieve high ionic conductivity, mechanicalflexibility, and improved safety in lithium-ion batteries. However, the ability to maintain high specific capacity for an extended lifetime is a difficult challenge. This investigation quantifies the viscoelastic characteristics of a particle-loaded polyethylene oxide (PEO) gel, under compression that mimics volumetric changes during charging. The hypothesis of this investigation is that the addition of a low concentration of rigid particles into a polymer gel electrolyte may either increase or decrease stiffness of the composite, depending on whether or not the particles interact with the polymer matrix. Titanium dioxide (TiO2) and tantalum-doped Li7La3Zr2O12 (LLZTO) were chosen as representative ceramic materials. Compressive stress was measured real-time under prescribed loading conditions using a piezo actuator, a high-sensitivity load cell, and an optical-grating displacement sensor. Experimental measurements revealed a two-fold increase in relaxation time constant between PEO alone and LLZTO-loaded PEO. In contrast, the addition of TiO2 particles of similar size and concentration reduced the time constant by nearly 80%. These experiments provide insights on how the mechanical stiffness of composite electrolytes can affect time-dependent stresses, and thereby influence long-term electrochemical performance of lithium-ion batteries.