Design and fabrication of high power microbatteries and high specific strength cellular solids from bicontinuous microporous hierarchical materials

An emerging paradigm in engineering design is the development of materials by constructing hierarchical assemblies of simple building blocks into complex architectures that address physics at multiple length scales. These hierarchical materials are increasingly important for the next generation of mechanical, electrical, chemical, and biological technologies. However, fabricating hierarchical materials with nm control over multiple chemistries in a scalable fashion is a challenge yet to be overcome. This dissertation reports the design and fabrication of hierarchical microbattery electrodes that demonstrate unprecedented power density as well as hierarchical cellular solids with controllable modulus and high specific strength. Self-assembly, electrodeposition and microfabrication enable the fabrication of microbatteries with hierarchical electrodes. The three-dimensional bicontinuous interdigitated microelectrode architecture improves power performance by simultaneously reducing ion and electron transport distances through the anode, cathode, and electrolyte. The microbattery power densities are up to 7.4 mW cm-2 μm-1, which equals or exceeds that of the best supercapacitors and which is 2000 times higher than that of other microbatteries. A one dimensional electrochemical model of the microbatteries enables the study of physical processes that limit power performance. Lithium diffusion through the solid cathode most significantly limits the amount of energy extracted at high power density. Experimentally-validated design rules optimize and characterize the battery architecture for high power performance without the need for multiphysics based simulations. Electrochemical deposition techniques improve the microbattery energy density while maintaining high power density by allowing high volume fractions of electrochemically active material to be integrated into the high power architectures. The microbattery energy densities are up to 45.5 µWh cm-2 µm-1, which is greater than previously reported three-dimensional microbatteries and comparable to commercially available lithium-based batteries. This dissertation also demonstrates the fabrication of 3D regular macroporous microcantilevers with Young’s moduli that can be varied from 2.0 to 44.3 GPa. The porosity and deformation mode of the hierarchical material, which depends on the pore structure, determine the Young’s moduli of the microcantilevers. The template technique allows 3D spatial control of the ordered porous structure and the ability to use a broad set of materials, demonstrated with nickel and alumina microcantilevers. Self-assembly and electrodeposition enable the scaling of the hierarchical microcantilever material to areas larger than cm2. The large area nickel cellular solids have specific compressive strengths up to 0.23 MPa / (kg  m−3). The specific strength is greater than most high strength steels and titanium alloys and is due to the size strengthening effect of the nanometer scale struts in the porous architecture. The scalable fabrication and detailed characterization of the large area cellular solids provide a route for testing high strength cellular materials in a broader set of engineering applications not available to previous techniques whose material dimensions are limited to tens of micrometers

Proximity and Visuotactile Point Cloud Fusion for Contact Patches in Extreme Deformation

Equipping robots with the sense of touch is critical to emulating the capabilities of humans in real world manipulation tasks. Visuotactile sensors are a popular tactile sensing strategy due to data output compatible with computer vision algorithms and accurate, high resolution estimates of local object geometry. However, these sensors struggle to accommodate high deformations of the sensing surface during object interactions, hindering more informative contact with cm-scale objects frequently encountered in the real world. The soft interfaces of visuotactile sensors are often made of hyperelastic elastomers, which are difficult to simulate quickly and accurately when extremely deformed for tactile information. Additionally, many visuotactile sensors that rely on strict internal light conditions or pattern tracking will fail if the surface is highly deformed. In this work, we propose an algorithm that fuses proximity and visuotactile point clouds for contact patch segmentation that is entirely independent from membrane mechanics. This algorithm exploits the synchronous, high-res proximity and visuotactile modalities enabled by an extremely deformable, selectively transmissive soft membrane, which uses visible light for visuotactile sensing and infrared light for proximity depth. We present the hardware design, membrane fabrication, and evaluation of our contact patch algorithm in low (10%), medium (60%), and high (100%+) membrane strain states. We compare our algorithm against three baselines: proximity-only, tactile-only, and a membrane mechanics model. Our proposed algorithm outperforms all baselines with an average RMSE under 2.8mm of the contact patch geometry across all strain ranges. We demonstrate our contact patch algorithm in four applications: varied stiffness membranes, torque and shear-induced wrinkling, closed loop control for whole body manipulation, and pose estimation

High precision electrohydrodynamic printing of polymer onto microcantilever sensors

This thesis reports electrohydrodynamic jet printing to deposit 2 ??? 27 um diameter polymer droplets onto microcantilever sensors. The polymer droplets were deposited as single droplets or organized patterns, with sub-??m control over droplet diameter and position. The droplet size could be controlled through a pulse-modulated source voltage, while droplet position was controlled using a positioning stage. Gravimetry analyzed the polymer droplets by examining the shift in microcantilever resonance frequency resulting from droplet deposition. The resonance shift of 50 - 4130 Hz corresponded to a polymer mass of 4.5 - 135 pg. The electrohydrodynamic method is a precise way to deposit multiple materials onto micromechanical sensors with greater resolution and repeatability than current methods

Computer‐Free Autonomous Navigation and Power Generation Using Electro‐Chemotaxis

Computer‐free autonomous decision making based on environmental cues provides exciting alternatives to classic control systems for robots and smart materials. Although this functionality has been studied in microswimmers and active colloids where energy in the surrounding liquid is prevalent, there are no devices that can provide sufficient power from environmental chemicals to move and steer larger scale robots and vehicles in dry environments. This work overcomes this limitation with an environmentally controlled voltage source (ECVS) that, when directly attached to electric motors on a vehicle, can increase the energy available to the vehicle and provide computer‐free autonomous navigation toward chemical fuels in the environment and away from hazards. The ECVS uses electrochemistry to extract power from the chemical fuels, and the vehicle avoids hazards that reduce the output voltage or electrochemical kinetics. Two ECVSs can also be arranged in series or parallel to perform logical functions based on the chemicals in contact with the ECVSs. This work presents a new method to simultaneously steer and power vehicles and robots without computers by directly responding to a wide variety of chemical fields in their environment using electrochemistry