MHD Thruster with Capillary-Porous Electrodes

Plasma Physics Reports - Capillary-porous electrodes for plasma MHD devices are considered. The electrodes can be continuously renewable and allow one to use a scheme of the inverted MHD generator...     

Silicon Composite Electrodes with Dynamic Ionic Bonding

Silicon (Si) composite electrodes are developed with increased cycle lifetimes and reliability through dynamic ionic bonding between active Si nanoparticles and a polymer binder. Amine groups are covalently attached to Si nanoparticles via surface functionalization. Si composite electrodes are fabricated by combining the Si nanoparticles with a poly(acrylic acid) (PAA) binder. The formation of ionic bonds between amine groups on Si particles and carboxylic acid groups on the PAA binder is characterized by X‐ray photoelectron spectroscopy and Raman spectroscopy. Si composite anodes with ionic bonding demonstrate long term cycling stability with capacity retention of 80% at 400 cycles at a current density of 2.1 A g^?1 and good rate capability. The dynamic ionic bonds effectively mitigate the deterioration of electrical interfaces in the composite anodes as suggested by stable impedance over 300 cycles.     

Picoinjection of Microfluidic Drops Without Metal Electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.     

Liquid Metal Electrodes for Energy Storage Batteries

The increasing demands for integration of renewable energy into the grid and urgently needed devices for peak shaving and power rating of the grid both call for low‐cost and large‐scale energy storage technologies. The use of secondary batteries is considered one of the most effective approaches to solving the intermittency of renewables and smoothing the power fluctuations of the grid. In these batteries, the states of the electrode highly affect the performance and manufacturing process of the battery, and therefore leverage the price of the battery. A battery with liquid metal electrodes is easy to scale up and has a low cost and long cycle life. In this progress report, the state‐of‐the‐art overview of liquid metal electrodes (LMEs) in batteries is reviewed, including the LMEs in liquid metal batteries (LMBs) and the liquid sodium electrode in sodium‐sulfur (Na–S) and ZEBRA (Na–NiCl₂) batteries. Besides the LMEs, the development of electrolytes for LMEs and the challenge of using LMEs in the batteries, and the future prospects of using LMEs are also discussed.     

Multimodal Nanoscale Tomographic Imaging for Battery Electrodes

Accurate representations of the 3D structure within a lithium‐ion battery are key to understanding performance limitations. However, obtaining exact reconstructions of electrodes, where the active particles, the carbon black and polymeric binder domain, and the pore space are visualized is challenging. Here, it is shown that multimodal imaging can be used to overcome this challenge. High‐resolution ptychographic X‐ray computed tomography are combined with lower resolution but higher contrast transmission X‐ray tomographic microscopy to obtain 3D reconstructions of pristine and cycled graphite‐silicon composite electrodes. This cross‐correlation enables quantitative analysis of the surface of active particles, including the heterogeneity of carbon‐black and binder domain and solid‐electrolyte interphase coverage. Capturing the active particles as well as the carbon black‐binder domain allows using these segmented structures for electrochemical simulations to highlight the influence of the particle embedding on local state of charge heterogeneities.     

Plasma Railgun with Capillary–Porous Electrodes

Plasma Physics Reports - A scheme of a spacecraft thruster based on pulsed plasma railgun with capillary–porous electrodes is proposed. Electrodes of this kind are renewable and do not...     

Lithium Intercalation Behavior in Multilayer Silicon Electrodes

Next generation lithium battery materials will require a fundamental shift from those based on intercalation to elements or compounds that alloy directly with lithium. Intermetallics, for instance, can electrochemically alloy to Li_4.4M (M = Si, Ge, Sn, etc.), providing order‐of‐magnitude increases in energy density. Unlike the stable crystal structure of intercalation materials, intermetallic‐based electrodes undergo dramatic volume changes that rapidly degrade the performance of the battery. Here, the energy density of silicon is combined with the structural reversibility of an intercalation material using a silicon/metal‐silicide multilayer. In operando X‐ray reflectivity confirms the multilayer's structural reversibility during lithium insertion and extraction, despite an overall 3.3‐fold vertical expansion. The multilayer electrodes also show enhanced long‐term cyclability and rate capabilities relative to a comparable silicon thin film electrode. This intercalation behavior found by dimensionally constraining silicon's lithiation promises applicability to a wide range of conversion reactions.     

Performing Behavioral Tasks in Subjects with Intracranial Electrodes

Patients having stereo-electroencephalography (SEEG) electrode, subdural grid or depth electrode implants have a multitude of electrodes implanted in different areas of their brain for the localization of their seizure focus and eloquent areas. After implantation, the patient must remain in the hospital until the pathological area of brain is found and possibly resected. During this time, these patients offer a unique opportunity to the research community because any number of behavioral paradigms can be performed to uncover the neural correlates that guide behavior. Here we present a method for recording brain activity from intracranial implants as subjects perform a behavioral task designed to assess decision-making and reward encoding. All electrophysiological data from the intracranial electrodes are recorded during the behavioral task, allowing for the examination of the many brain areas involved in a single function at time scales relevant to behavior. Moreover, and unlike animal studies, human patients can learn a wide variety of behavioral tasks quickly, allowing for the ability to perform more than one task in the same subject or for performing controls. Despite the many advantages of this technique for understanding human brain function, there are also methodological limitations that we discuss, including environmental factors, analgesic effects, time constraints and recordings from diseased tissue. This method may be easily implemented by any institution that performs intracranial assessments; providing the opportunity to directly examine human brain function during behavior.     

Electrochemical Stiffness Changes in Lithium Manganese Oxide Electrodes

In situ strain and stress measurements are performed on composite electrodes to monitor potential‐dependent stiffness changes in lithium manganese oxide (LiMn₂O₄). Lithium insertion and removal results in asynchronous strain and stress generation in the electrode. Electrochemical stiffness changes are calculated by combining coordinated stress and strain measurements. The electrode experiences dramatic changes in electrochemical stiffness due to potential‐dependent Li⁺ ion intercalation mechanisms. The development of stress in the early stages of delithiation (at ≈3.95 V) due to a kinetic barrier at the electrode surface gives rise to stiffness changes in the electrode. Strain generation due to phase transformations reduces stiffness in the electrode at 4.17 V during delithiation and at 4.11 V during lithiation. During lithiation, stress generation due to Coulombic repulsions between occupied and incoming Li⁺ ions leads to stiffening of the electrode at 3.96 V. The electrode also experiences greater changes in stiffness during delithiation compared to lithiation. These changes in electrochemical stiffness provide insight into the interplay between mechanical and electrochemical properties which control electrode response to lithiation and delithiation.