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. Stresspotential
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.
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Analytical Modeling and Simulation of the Blocked Force and Large Deformation of Multifunctional Segmented Lithium Ion Battery Unimorph Actuator
A self-powered, and self-actuating lithium ion battery (LIB) has
the potential to achieve large deformation while still maintaining
actuation force. The energy storage capability allows for
continual actuation without an external power source once
charged. Reshaping the actuator requires a nonuniform
distribution of charge and/or bending stiffness. Spatially
varying the state of charge and bending stiffness along the length
of a segmented unimorph configuration have the effect of
improving the tailorability of the deformed actuator. In this
paper, an analytical model is developed to predict the actuation
properties of the segmented unimorph beam to determine its
usefulness as an actuator. The model predicts the free deflection,
blocked deflection, and blocked force at the tip as a function of
spatially varying state of charge and bending stiffness. The main
contribution of the paper is the development of blocked
deflection over the length of the segmented unimorph, which has
not yet been considered in the literature. The model is verified
using experimental data and commercial finite element analysis.
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- Award ID(s):
- 1662055
- NSF-PAR ID:
- 10165898
- Date Published:
- Journal Name:
- Proc. ASME. SMASIS2019, ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, V001T06A004, September 9–11, 2019
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Magnetoactive elastomers (MAEs) are capable of large deformation, shape programming, and moderately large actuation forces when driven by an external magnetic field. These capabilities enable applications such as soft grippers, biomedical devices, and actuators. To facilitate complex shape deformation and enhanced range of motion, a unimorph can be designed with varying geometries, behave spatially varying multi-material properties, and be actuated with a non-uniform external magnetic field. To predict actuation performance under these complex conditions, an analytical model of a segmented MAE unimorph is developed based on beam theory with large deformation. The effect of the spatially-varying magnetic field is approximated using a segment-wise effective torque. The model accommodates spatially varying concentrations of magnetic particles and differentiates between the actuation mechanisms of hard and soft magnetic particles by accommodating different assumptions concerning the magnitude and direction of induced magnetization under a magnetic field. To validate the accuracy of the model predictions, four case studies are considered with various magnetic particles and matrix materials. Actuation performance is measured experimentally to validate the model for the case studies. The results show good agreement between experimental measurements and model predictions. A further parametric study is conducted to investigate the effects of the magnetic properties of particles and external magnetic fields on the free deflection. In addition, complex shape programming of the unimorph actuator is demonstrated by locally altering the geometric and material properties.
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Abstract 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.
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Abstract Silicon anodes have been demonstrated to provide significant actuation in addition to energy storage in lithium-ion batteries (LIBs). This work studies the optimization of 1D unimorph and bimorph actuators to achieve a target shape upon actuation. A 1D shape matching with design optimization is used to estimate the varied charge distribution along the length for a LIB actuator and thereby the effect of distance between electrodes in charging.
A genetic algorithm (GA) is used with actuation strain distribution as the design variable. The objective of the optimization is to shape-match by minimizing the shape error between a target shape and actuated shape, both defined by several points along the length.
The approach is experimentally validated by shape matching a notched unimorph target shape. A shape error of 1.5% is obtained. An optimized unimorph converges to an objective function of less than 0.029% of the length at full state of charge (SOC) for a 5-segment beam.
A second shape matching case study using a bimorph is investigated to showcase the tailorability of LIB actuators. The optimal bimorph achieves an objective function of less than 0.23% of the length for a design variable set of top and bottom actuation strain of an 8-segment beam. The actuated shape nearly matches the target shape by simultaneously activating top and bottom active layers to achieve the same differential actuation strain (the difference between top and bottom active layer actuation strain).
The results show that a bimorph actuator can achieve a given shape while also storing significantly more charge than is necessary to maintain a given complex shape. This demonstrates a strength of energy storage based actuators: excess energy can be stored within the actuator and can be expended without affecting the work done or the shape maintained by the actuator.
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null (Ed.)This research presents an experimental program executed to understand the strength and stiffness properties of hollow built-up glass compression members that are intended for use in the modular construction of all glass, compression-dominant, shell-type structures. The proposed compression-dominant geometric form has been developed using the methods of form finding and three-dimensional graphical statics. This research takes the first steps towards a new construction methodology for glass structures where individual hollow glass units (HGU) are assembled using an interlocking system to form large, compression-dominant, shell-type structures, thereby exploiting the high compression strength of glass. In this study, an individual HGU has an elongated hexagonal prism shape and consists of two deck plates, two long side plates, and four short side plates, as is shown in Figure 1. Connections between glass plates are made using a two-sided transparent structural adhesive tape. The test matrix includes four HGUs, two each fabricated with 1 mm and 2 mm thick adhesive tape. All samples are dimensioned 64 cm on the long axis of symmetry, 51 cm on the short axis of symmetry, and are 10 cm in width. Glass plates are all 10 mm thick annealed float glass with geometric fabrication done using 5-axis abrasive water jet cutting. HGU assembly is accomplished using 3D printed truing clips and results in a rigid three-dimensional glass frame. Testing was done with the HGU oriented such that load was introduced on the short side edges of the two deck plates, resulting in an asymmetric load-support condition. A soft interface material was used between the HGU and steel plates of the hydraulic actuator and support for the purpose of avoiding premature cracking from local stress concentrations on the glass edges at the load and support locations. Force was applied in displacement control at 0.25 mm/minute with a full array of displacement and strain sensors. Test results for load vs. center deck plate transverse deflection are shown in Figure 2. All samples failed explosively by flexural buckling with no premature cracking on the load and support edges of the deck plates. Strain and deformation data clearly show the presence of second-order behavior resulting from bending deformation perpendicular to the plane of the deck plates. In general, linear axial behavior transitions to nonlinear second-order behavior, with increasing rates in deflection and strain growth, ultimately ending in glass fracture on the tension surfaces of the buckled deck plates. The failure resulted in near-complete disintegration of the deck plates, but with no observable cracking in any side plates and a secure connection on all adhesive tape. Results of the experimental program clearly demonstrate the feasibility of using HGUs for modular construction of compression dominant all-glass shell-type structures. This method of construction can significantly reduce the self-weight of the structure, and it will inspire the use of sustainable materials in the construction of efficient structures.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1115/SMASIS2019-5560
