Enabling Rapid Charging Lithium Metal Batteries via Surface Acoustic Wave-Driven Electrolyte Flow

Surface Acoustic Wave-Driven Enhancement of Enzyme-Linked Immunosorbent Assays: ELISAW

Enzyme-linked immunosorbent assays (ELISAs) are widely used in biology and clinical diagnosis. Relying on antigen-antibody interaction through diffusion, the standard ELISA protocol can be time-consuming, preventing its use in rapid diagnostics. We present a time-saving and more sensitive ELISA without changing the standard setup and protocol, using surface acoustic waves (SAWs) to enhance performance. Each step of the assay, from the initial antibody binding onto the walls of the well plate to the target analyte molecules' binding for detection─except, notably, for the blocking step─is improved principally via acoustic streaming-driven advection. Using SAWs, the time required for one step of an example ELISA is reduced from 60 to 15 min to achieve the same binding amount. By extending the duration of SAW exposure to 20 min, the sensitivity can be significantly improved over the 60 min, 35 °C ELISA without SAWs. It is also possible to confer beneficial improvements to bead-based ELISA by combining it with SAWs to further reduce the time required for binding to 2 min. By significantly increasing the speed of ELISA, its utility may be improved for a wide range of point-of-care diagnostics applications.

From Liquid to Solid-State Lithium Metal Batteries: Fundamental Issues and Recent Developments

The widespread adoption of lithium-ion batteries has been driven by the proliferation of portable electronic devices and electric vehicles, which have increasingly stringent energy density requirements. Lithium metal batteries (LMBs), with their ultralow reduction potential and high theoretical capacity, are widely regarded as the most promising technical pathway for achieving high energy density batteries. In this review, we provide a comprehensive overview of fundamental issues related to high reactivity and migrated interfaces in LMBs. Furthermore, we propose improved strategies involving interface engineering, 3D current collector design, electrolyte optimization, separator modification, application of alloyed anodes, and external field regulation to address these challenges. The utilization of solid-state electrolytes can significantly enhance the safety of LMBs and represents the only viable approach for advancing them. This review also encompasses the variation in fundamental issues and design strategies for the transition from liquid to solid electrolytes. Particularly noteworthy is that the introduction of SSEs will exacerbate differences in electrochemical and mechanical properties at the interface, leading to increased interface inhomogeneity-a critical factor contributing to failure in all-solid-state lithium metal batteries. Based on recent research works, this perspective highlights the current status of research on developing high-performance LMBs.

Applications of remote epitaxy and van der Waals epitaxy

Epitaxy technology produces high-quality material building blocks that underpin various fields of applications. However, fundamental limitations exist for conventional epitaxy, such as the lattice matching constraints that have greatly narrowed down the choices of available epitaxial material combinations. Recent emerging epitaxy techniques such as remote and van der Waals epitaxy have shown exciting perspectives to overcome these limitations and provide freestanding nanomembranes for massive novel applications. Here, we review the mechanism and fundamentals for van der Waals and remote epitaxy to produce freestanding nanomembranes. Key benefits that are exclusive to these two growth strategies are comprehensively summarized. A number of original applications have also been discussed, highlighting the advantages of these freestanding films-based designs. Finally, we discuss the current limitations with possible solutions and potential future directions towards nanomembranes-based advanced heterogeneous integration.

Modeling fast acoustic streaming: Steady-state and transient flow solutions

Traditionally, acoustic streaming is assumed to be a steady-state, relatively slow fluid response to passing acoustic waves. This assumption, the so-called slow streaming assumption, was made over a century ago by Lord Rayleigh. It produces a tractable asymptotic perturbation analysis from the nonlinear governing equations, separating the acoustic field from the acoustic streaming that it generates. Unfortunately, this assumption is often invalid in the modern microacoustofluidics context, where the fluid flow and acoustic particle velocities are comparable. Despite this issue, the assumption is still widely used today, as there is no suitable alternative. We describe a mathematical method to supplant the classic approach and properly treat the spatiotemporal scale disparities present between the acoustics and remaining fluid dynamics. The method is applied in this work to well-known problems of semi-infinite extent defined by the Navier-Stokes equations, and preserves unsteady fluid behavior driven by the acoustic wave. The separation of the governing equations between the fast (acoustic) and slow (hydrodynamic) spatiotemporal scales are shown to naturally arise from the intrinsic properties of the fluid under forcing, not by arbitrary assumption beforehand. Solution of the unsteady streaming field equations provides physical insight into observed temporal evolution of bulk streaming flows that, to date, have not been modeled. A Burgers equation is derived from our method to represent unsteady flow. By then assuming steady flow, a Riccati equation is found to represent it. Solving these equations produces direct, concise insight into the nonlinearity of the acoustic streaming phenomenon alongside an absolute, universal upper bound of 50% for the energy efficiency in transducing acoustic energy input to the acoustic streaming energy output. Rigorous validation with respect to experimental and theoretical results from the classic literature is presented to connect this work to past efforts by many authors.

Ion Motor as a New Universal Strategy for the Boosting the Performance of Zn-Ion Batteries

The quiescent electrolyte causes serious concentration polarization and dendrite problems during the charging and discharging of the battery, which restricts the development of metal secondary batteries and flow batteries. Herein, we report a new concept of ion motors, with which the directional driving and uniformity of the electrolyte are realized to eliminate the concentration polarization and dendritic phenomenon for secondary metal batteries and flow batteries without additional external energy. In this study, a dendrite-free secondary metal battery with ion motors is constructed to eliminate a considerable concentration polarization voltage by a tiny induced counter electromotive force generated by Lorentz force, significantly improving the output power and energy efficiency of the battery. An actual pump-free flow battery with an ion motor is also assembled, which overcomes the problems of low energy efficiency and the complex structure caused by the traditional flow battery requiring 1-2 pumps to drive the electrolyte. The efficiency of ion motors to drive the electrolyte is hundreds of times higher than that of the mechanical pump. Therefore, the ion motor provides a universal strategy for designing more pump-free flow batteries and metal secondary batteries without the risk of dendrites in the future.

Solid Electrolyte Interphase Growth in Lithium Metal Cells With Normal Electrolyte Flow

In high energy density lithium metal batteries (LMBs), dendrite and solid electrolyte interphase (SEI) growth reduce safety and longevity, respectively. A stable SEI layer enables high efficiency cycling but continued SEI growth can lead to reduced capacity and coulombic efficiency. In this paper, we develop a steady-state model that predicts the effect of small advective electrolyte flow towards the lithium metal electrode on SEI growth during charging. For a fixed current density, increasing the electrolyte flow rate improves the coulombic efficiency and decreases SEI layer growth rate. Decreasing the charging current density at a constant flow rate also decreases the SEI layer growth rate. Low flow rates (μm/s) can increase coulombic efficiency by up to 6%. The sensitivity of the coulombic efficiency to plating and SEI layer reaction rates is also explored.

Ultrasound-Responsive Systems as Components for Smart Materials

Smart materials can respond to stimuli and adapt their responses based on external cues from their environments. Such behavior requires a way to transport energy efficiently and then convert it for use in applications such as actuation, sensing, or signaling. Ultrasound can carry energy safely and with low losses through complex and opaque media. It can be localized to small regions of space and couple to systems over a wide range of time scales. However, the same characteristics that allow ultrasound to propagate efficiently through materials make it difficult to convert acoustic energy into other useful forms. Recent work across diverse fields has begun to address this challenge, demonstrating ultrasonic effects that provide control over physical and chemical systems with surprisingly high specificity. Here, we review recent progress in ultrasound–matter interactions, focusing on effects that can be incorporated as components in smart materials. These techniques build on fundamental phenomena such as cavitation, microstreaming, scattering, and acoustic radiation forces to enable capabilities such as actuation, sensing, payload delivery, and the initiation of chemical or biological processes. The diversity of emerging techniques holds great promise for a wide range of smart capabilities supported by ultrasound and poses interesting questions for further investigations.

Polymorph Evolution Mechanisms and Regulation Strategies of Lithium Metal Anode under Multiphysical Fields

Lithium (Li) metal, a typical alkaline metal, has been hailed as the "holy grail" anode material for next generation batteries owing to its high theoretical capacity and low redox reaction potential. However, the uncontrolled Li plating/stripping issue of Li metal anodes, associated with polymorphous Li formation, "dead Li" accumulation, poor Coulombic efficiency, inferior cyclic stability, and hazardous safety risks (such as explosion), remains as one major roadblock for their practical applications. In principle, polymorphous Li deposits on Li metal anodes includes smooth Li (film-like Li) and a group of irregularly patterned Li (e.g., whisker-like Li (Li whiskers), moss-like Li (Li mosses), tree-like Li (Li dendrites), and their combinations). The nucleation and growth of these Li polymorphs are dominantly dependent on multiphysical fields, involving the ionic concentration field, electric field, stress field, and temperature field, etc. This review provides a clear picture and in-depth discussion on the classification and initiation/growth mechanisms of polymorphous Li from the new perspective of multiphysical fields, particularly for irregular Li patterns. Specifically, we discuss the impact of multiphysical fields' distribution and intensity on Li plating behavior as well as their connection with the electrochemical and metallurgical properties of Li metal and some other factors (e.g., electrolyte composition, solid electrolyte interphase (SEI) layer, and initial nuclei states). Accordingly, the studies on the progress for delaying/suppressing/redirecting irregular Li evolution to enhance the stability and safety performance of Li metal batteries are reviewed, which are also categorized based on the multiphysical fields. Finally, an overview of the existing challenges and the future development directions of metal anodes are summarized and prospected.

Practical microcircuits for handheld acoustofluidics

Acoustofluidics has promised to enable lab-on-a-chip and point-of-care devices in ways difficult to achieve using other methods. Piezoelectric ultrasonic transducers-as small as the chips they actuate-provide rapid fluid and suspended object transport. Acoustofluidic lab-on-chip devices offer a vast range of benefits in early disease identification and noninvasive drug delivery. However, their potential has long been undermined by the need for benchtop or rack-mount electronics. The piezoelectric ultrasonic transducers within require these equipment and thus acoustofluidic device implementation in a bedside setting has been limited. Here we detail a general process to enable the reader to produce battery or mains-powered microcircuits ideal for driving 1-300 MHz acoustic devices. We include the general design strategy for the circuit, the blocks that collectively define it, and suitable, specific choices for components to produce these blocks. We furthermore illustrate how to incorporate automated resonance finding and tracking, sensing and feedback, and built-in adjustability to accommodate devices' vastly different operating frequencies and powers in a single driver, including examples of fluid and particle manipulation typical of the needs in our discipline. With this in hand, the many groups active in lab-on-a-chip acoustofluidics can now finally deliver on the promise of handheld, point-of-care technologies.

Motile cells as probes for characterizing acoustofluidic devices

Acoustic microfluidics has emerged as a versatile solution for particle manipulation in medicine and biology. However, current technologies are largely confined to specialized research laboratories. The translation of acoustofluidics from research to clinical and industrial settings requires improved consistency and repeatability across different platforms. Performance comparisons will require straightforward experimental assessment tools that are not yet available. We introduce a method for characterizing acoustofluidic devices in real-time by exploiting the capacity of swimming microorganisms to respond to changes in their environment. The unicellular alga, Chlamydomonas reinhardtii, is used as an active probe to visualize the evolving acoustic pressure field within microfluidic channels and chambers. In contrast to more familiar mammalian cells, C. reinhardtii are simple to prepare and maintain, and exhibit a relatively uniform size distribution that more closely resembles calibration particles; however, unlike passive particles, these motile cells naturally fill complex chamber geometries and redistribute when the acoustic field changes or is turned off. In this way, C. reinhardtii cells offer greater flexibility than conventional polymer or glass calibration beads for in situ determination of device operating characteristics. To illustrate the technique, the varying spatial density and distribution of swimming cells are correlated to the acoustic potential to automatically locate device resonances within a specified frequency range. Peaks in the correlation coefficient of successive images not only identify the resonant frequencies for various geometries, but the peak shape can be related to the relative strength of the resonances. Qualitative mapping of the acoustic field strength with increasing voltage amplitude is also shown. Thus, we demonstrate that dynamically responsive C. reinhardtii enable real-time measurement and continuous monitoring of acoustofluidic device performance.

Suppression of dendrite growth by cross-flow in microfluidics

Formation of rough, dendritic deposits is a critical problem in metal electrodeposition processes and could occur in next-generation, rechargeable batteries that use metallic electrodes. Electroconvection, which originates from the coupling of the imposed electric field and a charged fluid near an electrode surface, is believed to be responsible for dendrite growth. However, few studies are performed at the scale of fidelity where root causes and effective strategies for controlling electroconvection and dendrite growth can be investigated in tandem. Using microfluidics, we showed that forced convection across the electrode surface (cross-flow) during electrodeposition reduced metal dendrite growth (97.7 to 99.4%) and delayed the onset of electroconvective instabilities. Our results highlighted the roles of forced convection in reducing dendrite growth and electroconvective instabilities and provided a route toward effective strategies for managing the consequences of instability in electrokinetics-based processes where electromigration dominates ion diffusion near electrodes.

Review on Li Deposition in Working Batteries: From Nucleation to Early Growth

Lithium (Li) metal is one of the most promising alternative anode materials of next-generation high-energy-density batteries demanded for advanced energy storage in the coming fourth industrial revolution. Nevertheless, disordered Li deposition easily causes short lifespan and safety concerns and thus severely hinders the practical applications of Li metal batteries. Tremendous efforts are devoted to understanding the mechanism for Li deposition, while the final deposition morphology tightly relies on the Li nucleation and early growth. Here, the recent progress in insightful and influential models proposed to understand the process of Li deposition from nucleation to early growth, including the heterogeneous model, surface diffusion model, crystallography model, space charge model, and Li-SEI model, are highlighted. Inspired by the abovementioned understanding on Li nucleation and early growth, diverse anode-design strategies, which contribute to better batteries with superior electrochemical performance and dendrite-free deposition behavior, are also summarized. This work broadens the horizon for practical Li metal batteries and also sheds light on more understanding of other important metal-based batteries involving the metal deposition process.

Building Better Li Metal Anodes in Liquid Electrolyte: Challenges and Progress

Li metal has been widely recognized as a promising anode candidate for high-energy-density batteries. However, the inherent limitations of Li metal, that is, the low Coulombic efficiency and dendrite issues, make it still far from practical applications. In short, the low Coulombic efficiency shortens the cycle life of Li metal batteries, while the dendrite issue raises safety concerns. Thanks to the great efforts of the research community, prolific fundamental understanding as well as approaches for mitigating Li metal anode safety have been extensively explored. In this Review, Li electrochemical deposition behaviors have been systematically summarized, and recent progress in electrode design and electrolyte system optimization is reviewed. Finally, we discuss the future directions, opportunities, and challenges of Li metal anodes.

Dynamical theory for the battery's electromotive force

We propose a dynamical theory of how the chemical energy stored in a battery generates the electromotive force (emf). In this picture, the battery's half-cell acts as an engine, cyclically extracting work from its underlying chemical disequilibrium. We show that the double layer at the electrode-electrolyte interface can exhibit a rapid self-oscillation that pumps an electric current, thus accounting for the persistent conversion of chemical energy into electrical work equal to the emf times the separated charge. We suggest a connection between this mechanism and the slow self-oscillations observed in various electrochemical cells, including batteries, as well as the enhancement of the current observed when ultrasound is applied to the half-cell. Finally, we propose more direct experimental tests of the predictions of this dynamical theory.