Li ion/vapor grown carbon fiber polymer actuators show higher performance than single-walled carbon nanotube polymer actuators

Abstract

The effects of Li tetrafluoroborate (Li[BF4]) and lithium bis(trifluoromethanesulfonyl)imide (Li[TFSI]) salts on the electrochemical and electromechanical properties of an actuator using a poly(vinylidene fluoride-co-hexafluoropropylene)-supported vapor grown carbon fiber (VGCF)/ionic liquid (IL) gel electrode formed without ultrasonication were investigated. At a slow sweep rate of 1 mV s−1, the measured double-layer capacitance values for the VGCF/Li[X]/IL actuator were in the range of 20.0–42.3 F g−1, and were larger than that for an IL-only actuator. The capacitance was found to increase with the Li[BF4] content, but was independent of the Li[TFSI] content. All of the VGCF/Li[X]/IL actuators exhibited a larger amount of strain than IL-only actuators, and for a VGCF/Li[TFSI]/EMI[TFSI] actuator with a Li[TFSI]/EMI[TFSI] molar ratio of 1.0, the maximum strain was greater than that for an IL actuator containing single-walled carbon nanotubes. Moreover, the frequency dependence of the displacement response for the VGCF/Li[X]/IL actuators was successfully simulated using an electrochemical kinetic model, similar to the case for SWCNT and VGCF based actuators containing metal oxide. The results yielded the strain in the low-frequency limit in addition to the time constant of the response.