Enhanced Low-Temperature Performance of Li–CFx Batteries

Abstract

This work describes the continued examination of the low-temperature performance of the Li–CFx electrochemical couple in a −40°C or colder environment. Previously, the efficacy of subfluorinated CFx (SFCFx) cathode active materials was demonstrated; preliminary results indicated that the material was functional at rates up to C/10 at −40°C. However, there were often substantial voltage fluctuations during discharge, accompanied with inconsistent capacity yields and sometimes dramatic polarization events. In the research described herein, an investigation of various electrolyte and cathode compositions was conducted in an effort to optimize performance. In particular, several different electrolyte solvent formulations were examined using a salt content of either 1 or 0.5 M LiBF4. A further modification consisted of addition of an anion receptor to the electrolyte that was intended to be a LiF-solvating agent. The most promising electrolyte was tested with several different SFCFx compositions created using either graphitic or multiwall nanotube precursor materials. Electrochemical evaluation showed that the best SFCFx-based test cells were able to deliver specific capacity values up to five times greater than control cells (containing conventional CF1.08 powder) at −40°C under discharge currents as high as C/5 with composite electrodes thicker than 100 µm.

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