Kathleen Maleski

Nanodiamonds suppress the growth of lithium dendrites

Lithium metal has been regarded as the future anode material for high-energy-density rechargeable batteries due to its favorable combination of negative electrochemical potential and high theoretical capacity. However, uncontrolled lithium deposition during lithium plating/stripping results in low Coulombic efficiency and severe safety hazards. Herein, we report that nanodiamonds work as an electrolyte additive to co-deposit with lithium ions and produce dendrite-free lithium deposits. First-principles calculations indicate that lithium prefers to adsorb onto nanodiamond surfaces with a low diffusion energy barrier, leading to uniformly deposited lithium arrays. The uniform lithium deposition morphology renders enhanced electrochemical cycling performance. The nanodiamond-modified electrolyte can lead to a stable cycling of lithium | lithium symmetrical cells up to 150 and 200 h at 2.0 and 1.0 mA cm–2, respectively. The nanodiamond co-deposition can significantly alter the lithium plating behavior, affording a promising route to suppress lithium dendrite growth in lithium metal-based batteries.Lithium metal is an ideal anode material for rechargeable batteries but suffer from the growth of lithium dendrites and low Coulombic efficiency. Here the authors show that nanodiamonds serve as an electrolyte additive to co-deposit with lithium metal and suppress the formation of dendrites.

Metallic Ti3C2Tx MXene Gas Sensors with Ultrahigh Signal-to-Noise Ratio

Achieving high sensitivity in solid-state gas sensors can allow the precise detection of chemical agents. In particular, detection of volatile organic compounds (VOCs) at the parts per billion (ppb) level is critical for the early diagnosis of diseases. To obtain high sensitivity, two requirements need to be simultaneously satisfied: (i) low electrical noise and (ii) strong signal, which existing sensor materials cannot meet. Here, we demonstrate that 2D metal carbide MXenes, which possess high metallic conductivity for low noise and a fully functionalized surface for a strong signal, greatly outperform the sensitivity of conventional semiconductor channel materials. Ti3C2Tx MXene gas sensors exhibited a very low limit of detection of 50-100 ppb for VOC gases at room temperature. Also, the extremely low noise led to a signal-to-noise ratio 2 orders of magnitude higher than that of other 2D materials, surpassing the best sensors known. Our results provide insight in utilizing highly functionalized metallic sensing channels for developing highly sensitive sensors.

Saturable Absorption in 2D Ti3C2 MXene Thin Films for Passive Photonic Diodes

MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3 CNTx (Tx represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti3 C2 Tx thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, it is found that the SA behavior in Ti3 C2 Tx MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti3 C2 Tx MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti3 C2 Tx is found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti3 C2 Tx MXenes, a Ti3 C2 Tx MXene-based photonic diode that breaks time-reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated.

Rheological Characteristics of 2D Titanium Carbide (MXene) Dispersions: A Guide for Processing MXenes

Understanding the rheological properties of two-dimensional (2D) materials in suspension is critical for the development of various solution processing and manufacturing techniques. 2D carbides and nitrides (MXenes) constitute one of the largest families of 2D materials with >20 synthesized compositions and applications already ranging from energy storage to medicine to optoelectronics. However, in spite of a report on clay-like behavior, not much is known about their rheological response. In this study, rheological behavior of single- and multilayer Ti3C2T x in aqueous dispersions was investigated. Viscous and viscoelastic properties of MXene dispersions were studied over a variety of concentrations from colloidal dispersions to high loading slurries, showing that a multilayer MXene suspension with up to 70 wt % can exhibit flowability. Processing guidelines for the fabrication of MXene films, coatings, and fibers have been established based on the rheological properties. Surprisingly, high viscosity was observed at very low concentrations for solutions of single-layer MXene flakes. Single-layer colloidal solutions were found to exhibit partial elasticity even at the lowest tested concentrations (<0.20 mg/mL) due to the presence of strong surface charge and excellent hydrophilicity of MXene, making them amenable to fabrication at dilute concentrations. Overall, the findings of this study provide fundamental insights into the rheological response of this quickly growing 2D family of materials in aqueous environments as well as offer guidelines for processing of MXenes.

Two-Dimensional Ti3C2 MXene for High-Resolution Neural Interfaces

High-resolution neural interfaces are essential tools for studying and modulating neural circuits underlying brain function and disease. Because electrodes are miniaturized to achieve higher spatial resolution and channel count, maintaining low impedance and high signal quality becomes a significant challenge. Nanostructured materials can address this challenge because they combine high electrical conductivity with mechanical flexibility and can interact with biological systems on a molecular scale. Unfortunately, fabricating high-resolution neural interfaces from nanostructured materials is typically expensive and time-consuming and does not scale, which precludes translation beyond the benchtop. Two-dimensional (2D) Ti3C2 MXene possesses a combination of remarkably high volumetric capacitance, electrical conductivity, surface functionality, and processability in aqueous dispersions distinct among carbon-based nanomaterials. Here, we present a high-throughput microfabrication process for constructing Ti3C2 neuroelectronic devices and demonstrate their superior impedance and in vivo neural recording performance in comparison with standard metal microelectrodes. Specifically, when compared to gold microelectrodes of the same size, Ti3C2 electrodes exhibit a 4-fold reduction in interface impedance. Furthermore, intraoperative in vivo recordings from the brains of anesthetized rats at multiple spatial and temporal scales demonstrate that Ti3C2 electrodes exhibit lower baseline noise, higher signal-to-noise ratio, and reduced susceptibility to 60 Hz interference than gold electrodes. Finally, in neuronal biocompatibility studies, neurons cultured on Ti3C2 are as viable as those in control cultures, and they can adhere, grow axonal processes, and form functional networks. Overall, our results indicate that Ti3C2 MXene microelectrodes have the potential to become a powerful platform technology for high-resolution biological interfaces.