State-of-the-art rechargeable batteries are incapable of providing the high energy densities required in order to free the device-implanted patient from a tethered external power source. The ability to provide a left ventricular assisted device patient or implanted artificial heart patient with significant more time "off-tether" would greatly improve his or her quality of life. Therefore, the aim of our proposed research is to develop advanced electrolyte materials and formulations thereof that would safely enable the extraction of more energy from an implanted lithium- ion (Li-ion) rechargeable battery. Specifically, we proposed to prepare and evaluate a group of gel polymer electrolytes comprising ionic liquids that are non-flammable, electrochemically stable, and thermally robust. Li-ion cells incorporating the new electrolytes will be built and tested with a focus on establishing the intrinsic stability of the gel polymer electrolyte in direct contact with highly delithiated cathode materials. To this end we will employ differential scanning calorimetry to determine the onset of thermochemical reactions between cathode material and electrolyte as a function of the cathode's state of charge. If successful, we will embark on a program to build and quality prototype Li-ion batteries that will allow implanted devices to safely operate on internal power for longer period of time. PROPOSED COMMERCIAL APPLICATIONS: Not Available