Harnessing the actuation potential of solid-state intercalation compounds

High-strain, high-force mechanical actuation technologies are desirable for numerous applications ranging from microelectromechanical systems (MEMS) to large-scale smart structures that are able to change shape to optimize performance. Here we show that electrochemical intercalation of inorganic compounds of high elastic modulus offers a low-voltage mechanism (less than 5 V) with intrinsic energy density approaching that of hydraulics and more than a hundred times greater than that of existing field-operated mechanisms, such as piezostriction and magnetostriction. Exploitation of the reversible crystallographic strains (several percent) of intercalation compounds while under high stress is key to realization of the available energy. Using a micromachined actuator design, we test the strain capability of oriented graphite due to electrochemical lithiation under stresses up to 200 MPa. We further demonstrate that simultaneous electrochemical expansion of the LiCoO2/graphite cathode/ anode couple can be exploited for actuation under stresses up to similar to 20 MPa in laminated macroscopic composite actuators of similar design to current lithium-ion batteries. While the transport-limited actuation mechanism of these devices results in intrinsically slower actuation compared to most ferroic materials, we demonstrate up to 6.7 mHz (150 s) cyclic actuation in a laminated actuator designed for a high charge/discharge rate. The potential for a new class of high-strain, high-force, moderate-frequency actuators suitable for a broad range of applications is suggested.