Eric Kazyak

Dendrites and Pits: Untangling the Complex Behavior of Lithium Metal Anodes through Operando Video Microscopy

Enabling ultra-high energy density rechargeable Li batteries would have widespread impact on society. However the critical challenges of Li metal anodes (most notably cycle life and safety) remain unsolved. This is attributed to the evolution of Li metal morphology during cycling, which leads to dendrite growth and surface pitting. Herein, we present a comprehensive understanding of the voltage variations observed during Li metal cycling, which is directly correlated to morphology evolution through the use of operando video microscopy. A custom-designed visualization cell was developed to enable operando synchronized observation of Li metal electrode morphology and electrochemical behavior during cycling. A mechanistic understanding of the complex behavior of these electrodes is gained through correlation with continuum-scale modeling, which provides insight into the dominant surface kinetics. This work provides a detailed explanation of (1) when dendrite nucleation occurs, (2) how those dendrites evolve as a function of time, (3) when surface pitting occurs during Li electrodissolution, (4) kinetic parameters that dictate overpotential as the electrode morphology evolves, and (5) how this understanding can be applied to evaluate electrode performance in a variety of electrolytes. The results provide detailed insight into the interplay between morphology and the dominant electrochemical processes occurring on the Li electrode surface through an improved understanding of changes in cell voltage, which represents a powerful new platform for analysis.

Dead lithium: mass transport effects on voltage, capacity, and failure of lithium metal anodes

Improvement of the performance of Li metal anodes is critical to enable high energy density rechargeable battery systems beyond Li-ion. However, a complete mechanistic understanding of electrode overpotential variations that occur during extended cycling of Li metal is lacking. Herein, we demonstrate that when using a Li metal electrode, the dynamic changes in voltage during extended cycles can be increasingly attributed to mass transport. It is shown that these mass transport effects arise as a result of dead Li accumulation at the Li metal electrode, which introduces a tortuous pathway for Li-ion transport. In Li–Li symmetric cells, mass transport effects cause the shape of the galvanostatic voltage response to change from “peaking” to “arcing”, along with an increase in total electrode overpotential. The continued accumulation of dead Li is also conclusively shown to directly cause capacity fade and rapid “failure” of Li–LCO full cells containing Li metal anodes. This work provides detailed insights into the coupled relationships between cycling, interphase morphology, mass transport and the overall cell performance. Furthermore, this work helps underscore the potential of Li–Li symmetric cells as a powerful analytical tool for understanding the effects of Li metal electrodes in full cell batteries.

Rational Design of Hyperbranched Nanowire Systems for Tunable Superomniphobic Surfaces Enabled by Atomic Layer Deposition

Superomniphobic surfaces display contact angles of θ* > 150° and low contact angle hysteresis with virtually all high and low surface tension liquids. The introduction of hierarchical scales of texture can increase the contact angles and decrease the contact angle hysteresis of superomniphobic surfaces by reducing the solid-liquid contact area. Thus far, it has not been possible to fabricate superomniphobic surfaces with three or more hierarchical scales of texture where the size, spacing, and angular orientation of features within each scale of texture can be independently varied and controlled. Here, we report a method for tunable control of geometry in hyperbranched ZnO nanowire (NW) structures, which in turn enables the rational design and fabrication of superomniphobic surfaces. Branched NWs with tunable density and orientation were grown via a sequential hydrothermal process, in which atomic layer deposition was used for NW seeding, disruption of epitaxy, and selective blocking of NW nucleation. This approach allows for the rational design and optimization of three-level hierarchical structures, in which the geometric parameters of each level of hierarchy can be individually controlled. We demonstrate the coupled relationships between geometry and contact angles for a variety of liquids, which is supported by mathematical models. The highest performing superomniphobic surface was designed with three levels of hierarchy and achieved the following advancing/receding contact angles with water 172°/170°, hexadecane 166°/156°, octane 162°/145°, and heptane 160°/130°.

Biotemplated Morpho Butterfly Wings for Tunable Structurally Colored Photocatalysts

Morpho sulkowskyi butterfly wings contain naturally occurring hierarchical nanostructures that produce structural coloration. The high aspect ratio and surface area of these wings make them attractive nanostructured templates for applications in solar energy and photocatalysis. However, biomimetic approaches to replicate their complex structural features and integrate functional materials into their three-dimensional framework are highly limited in precision and scalability. Herein, a biotemplating approach is presented that precisely replicates Morpho nanostructures by depositing nanocrystalline ZnO coatings onto wings via low-temperature atomic layer deposition (ALD). This study demonstrates the ability to precisely tune the natural structural coloration while also integrating multifunctionality by imparting photocatalytic activity onto fully intact Morpho wings. Optical spectroscopy and finite-difference time-domain numerical modeling demonstrate that ALD ZnO coatings can rationally tune the structural coloration across the visible spectrum. These structurally colored photocatalysts exhibit an optimal coating thickness to maximize photocatalytic activity, which is attributed to trade-offs between light absorption and catalytic quantum yield with increasing coating thickness. These multifunctional photocatalysts present a new approach to integrating solar energy harvesting into visually attractive surfaces that can be integrated into building facades or other macroscopic structures to impart aesthetic appeal.

Atomic layer deposition and first principles modeling of glassy Li3BO3–Li2CO3 electrolytes for solid-state Li metal batteries

Thin-film lithium solid electrolytes can serve as passivation layers, interfacial coatings, and enable 3D solid-state batteries. Here we present an Atomic Layer Deposition (ALD) process for synthesis of amorphous lithium borate-carbonate (LBCO) films. These films exhibit ionic conductivities up to 2.2 × 10−6 S cm−1, six times greater than previously reported for any ALD solid electrolyte. First principles calculations trace the high conductivity to contributions from enhanced rotational motion of the carbonate and borate anions achieved by precise control of Li and C content by ALD. The high conductivity, coupled with a wide band gap and electrochemical stability window, leads to a total area specific resistance (ASR) of 0.9999 from 0–6 volts vs. Li metal. The LBCO ALD solid electrolyte exhibits stability upon exposure to air, and in contact with both Li metal anodes and cathode materials. Thin-film full cells containing Li metal electrodes exhibit high coulombic efficiency for over 150 cycles with no capacity fading. These characteristics make glassy LBCO a promising new material for solid-state Li metal batteries.