Analytical Modeling of a Multifunctional Segmented Lithium Ion Battery Unimorph Actuator

Abstract

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.