Lithium-ion batteries (LIBs) are able to achieve large deformation and high actuation force when using a unimorph configuration and a silicon composite anode. Distribution of charge to different segments allows for shape change with only small parasitic losses due to internal resistance. A unique attribute of LIB actuators are their ability to maintain actuation shape. The actuation mechanism also requires no power to be consumed to maintain the deformed shape. Segmenting the unimorph improves the customizability and allows for spatial variation of the unimorph parameters. Spatially varying the charge and thickness of the unimorph along the length improves the range of motion and complex shapes achievable by this design. Spatially varying the thickness of the unimorph specifically allows for improved blocked force and actuation force per volume. An analytical model is developed to predict several key actuator metrics. Free deflection is found for a variety of example cases. Blocked deflection and blocked force are also found using a novel modified equivalent end moment method. Actuation force is found using a combination of both the free deflection and blocked force equations herein developed. Euler–Bernoulli beam theory is used, including the effects of beam segmentation and curvature shortening. This model and a commercial finite element analysis simulation are compared and experimentally verified.

Among anode materials for Li-ion batteries, Si is known for high theoretical capacity, low cost, large volume change, relatively fast capacity fade and significant stress-potential coupling. This article shows that a Li(Ni0.5Co0.2Mn0.3)O2-Si battery can store energy, actuate with Si volume change and sense with stress-potential coupling. Experiments are conducted in an electrolyte-filled chamber with a glass window with [Formula: see text] cathodes and Si composite anodes. The Si anodes are single-side coated on Cu current collector with Si nanoparticles, polyacrylic acid binder and conductive carbon black in a porous composite structure. During charging, the battery stores energy, Li inserts in the cantilevered Si anodes and the cantilevers bend laterally. Discharging the battery releases the stored energy and straightens the Si cantilevers. Imposing deformation on the Si cantilevers at a fixed state of charge causes bending stress in the composite coating and a change in the open circuit potential. Testing at [Formula: see text] confirms that the Si composite responds to dynamic stress variations and with almost no phase lag, indicating the bandwidth of the stress-potential coupling in Si composite anodes is at least [Formula: see text].

Silicon composite anode-based lithium ion battery actuators have strong potential for large actuation strain, complex shape change, and large compliance tunability. This allows for actuators with potential to do work with no energy expenditure beyond parasitic losses to internal resistance. This paper studies a segmented bimorph actuator comprised of a silicon-based composite anode double-side coated on copper foil. The bimorph design allows for a nearly 360° range of motion in transverse bending and can double the capacity of the battery in comparison to a single side coated unimorph design. An Euler-Bernoulli model is developed to predict free deflection for a range of geometric configurations and states of charge of the bimorph. By modeling the charging of both active sides of the bimorph simultaneously, it is possible to achieve zero bending while still accommodating for the volumetric expansion of the silicon. The bimorph is able to achieve actuation in one given direction by charging each anode coating separately or maintaining a charge difference between the two coatings. The former method allows for the accommodated volumetric expansion of silicon while maintaining zero bending as in a conventional battery setup. The latter method allows for larger battery capacity and range of motion for a novel electrochemically-based actuation mechanism.

Silicon anodes in lithium ion batteries have high theoretical capacity and large volumetric expansion. In this paper, both characteristics are used in a segmented unimorph actuator consisting of several Si composite anodes on a copper current collector. Each unimorph segment is self-actuating during discharge and the discharge power can be provided to external circuits. With no external forces and zero current draw, the unimorph segments will maintain their actuated shape. Stress-potential coupling allows for the unimorph actuator to be self-sensing because bending changes the anodes’ potential. An analytical model is derived from a superposition of pure bending and extensional deformation forces and moments induced by the cycling of a Si anode. An approximately linear relationship between axial strain and state of charge of the anode drives the bending displacement of the unimorph. The segmented device consists of electrically insulated and individually controlled segments of the Si-coated copper foil to allow for variable curvature throughout the length of the beam. The model predicts the free deflection along the length of the beam and the blocked force. Tip deflection and blocked force are shown for a range of parameters including segment thicknesses, beam length, number of segments, and state of charge. The potential applications of this device include soft robots and dexterous 3D grippers.

Silicon is regarded as one of the most promising anode materials for lithium-ion batteries. Its high theoretical capacity (4000 mAh/g) has the potential to meet the demands of high-energy density applications, such as electric air and ground vehicles. The volume expansion of Si during lithiation is over 300%, indicating its promise as a large strain electrochemical actuator. A Si-anode battery is multifunctional, storing electrical energy and actuating through volume change by lithium-ion insertion. To utilize the property of large volume expansion, we design, fabricate, and test two types of Si anode cantilevers with bi-directional actuation: (a) bimorph actuator and (b) insulated double unimorph actuator. A transparent battery chamber is fabricated, provided with NCM cathodes, and filled with electrolyte. The relationship between state of charge and electrode deformation is measured using current integration and high-resolution photogrammetry, respectively. The electrochemical performance, including voltage versus capacity and Coulombic efficiency versus cycle number, is measured for several charge/discharge cycles. Both configurations exhibit deflections in two directions and can store energy. In case (a), the largest deflection is roughly 35% of the cantilever length. Twisting and unexpected bending deflections are observed in this case, possibly due to back-side lithiation, non-uniform coating thickness, and uneven lithium distribution. In case (b), the single silicon active coating layer can deflect 12 passive layers.