Nanoscale Investigation of Solid Electrolyte Interphase Inhibition on Li-Ion Battery MnO Electrodes via Atomic Layer Deposition of Al₂O₃

Application of a functional surface coating on Li-ion battery electrodes can potentially result in a significant enhancement of the lifespan of the battery cell. In particular, atomic layer deposition (ALD), which can create highly conformal ultrathin oxide films on many different electrodes has been shown to increase the cyclability in these systems. In this study, we explore the impact of such films on the formation of the solid electrolyte interphase (SEI), which may explain why these films show improvements in the cycling performance. Specifically, we characterize, using in situ scanning ion conductance microscopy and other ex situ surface characterization techniques, the SEI formed on ALD Al₂O₃ coated and uncoated MnO electrodes. We ascertain that ∼9 Å is the minimum thickness of ALD Al₂O₃ that will inhibit thick SEI formation. Furthermore, we show that the ALD surface coating is robust and prevents SEI formation for at least 100 cycles. Lastly, we investigated the differences between our in situ and ex situ measurements to help determine what artifacts can result that are due to post-processing for ex situ studies

Defect Evolution in Graphene upon Electrochemical Lithiation

Despite rapidly growing interest in the application of graphene in lithium ion batteries, the interaction of the graphene with lithium ions and electrolyte species during electrochemical cycling is not fully understood. In this work, we use Raman spectroscopy in a model system of monolayer graphene transferred on a Si(111) substrate and density functional theory (DFT) to investigate defect formation as a function of lithiation. This model system enables the early stages of defect formation to be probed in a manner previously not possible with commonly used reduced graphene oxide or multilayer graphene substrates. Using ex situ and Ar-atmosphere Raman spectroscopy, we detected a rapid increase in graphene defect level for small increments in the number of lithiation/delithiation cycles until the I­(D)<i>/</i>I­(G) ratio reaches ∼1.5–2.0 and the 2D peak intensity drops by ∼50%, after which the Raman spectra show minimal changes upon further cycling. Using DFT, the interplay between graphene topological defects and chemical functionalization is explored, thus providing insight into the experimental results. In particular, the DFT results show that defects can act as active sites for species that are present in the electrochemical environment such as Li, O, and F. Furthermore, chemical functionalization with these species lowers subsequent defect formation energies, thus accelerating graphene degradation upon cycling. This positive feedback loop continues until the defect concentration reaches a level where lithium diffusion through the graphene can occur in a relatively unimpeded manner, with minimal further degradation upon extended cycling. Overall, this study provides mechanistic insight into graphene defect formation during lithiation, thus informing ongoing efforts to employ graphene in lithium ion battery technology

Tunable Radiation Response in Hybrid Organic–Inorganic Gate Dielectrics for Low-Voltage Graphene Electronics

Solution-processed semiconductor and dielectric materials are attractive for future lightweight, low-voltage, flexible electronics, but their response to ionizing radiation environments is not well understood. Here, we investigate the radiation response of graphene field-effect transistors employing multilayer, solution-processed zirconia self-assembled nanodielectrics (Zr-SANDs) with ZrO_<i>x</i> as a control. Total ionizing dose (TID) testing is carried out in situ using a vacuum ultraviolet source to a total radiant exposure (RE) of 23.1 μJ/cm². The data reveal competing charge density accumulation within and between the individual dielectric layers. Additional measurements of a modified Zr-SAND show that varying individual layer thicknesses within the gate dielectric tuned the TID response. This study thus establishes that the radiation response of graphene electronics can be tailored to achieve a desired radiation sensitivity by incorporating hybrid organic–inorganic gate dielectrics