Reversible electrochemical compound formation has considerable potential to form the basis of a high-strain high-force multifunctional actuator technology. We present preliminary experimental demonstrations of the reversible work capability of solid-state electroplating. Our experimental test case is the volume expansion incurred during the reversible electrochemical formation of thin-film Li metal from a ceramic lithium ion storage medium, LiCoO2 as part of the standard operation of a state-of-the-art Li-ion battery. Reversible work is accomplished through the plating or stripping of the pure Li film against an external load. With the active portion of the structure as a basis, we observe ~10% strain against loads up to 2 MPa, with the load being limited by battery failure. No change in actuation characteristics is observed up to failure.
Graphite intercalation compounds are a class of materials systems formed as ions diffuse into a host graphite structure. The volume expansion associated with this process has been shown to be capable of performing work up to 3.8 MJ/m3. To evaluate GICs for solid state actuation, this study explores some factors affecting the rate at which the volume expansion occurs. Given that diffusion length has an exponential effect on rate, we tested a graphite paper comprised of 7-micron diameter PAN fibers. We found that the paper had ultimate strain and loading properties comparable to HOPG. The paper was cycled under various loads and temperatures to examine the strain rate and repeatability of the material. Testing showed a strong correlation between rate and temperature, while pressure had relatively little effect.