Delivering the full benefits of first principles calculations to battery materials demands the development of accurate and computationally-efficient electronic structure methods that incorporate the effects of the electrolyte environment and electrode potential.Realistic electrochemical interfaces containing polar surfaces are beyond the regime of validity of existing continuum solvation theories developed for molecules, due to the presence of significantly stronger electric fields. We present an ab initio theory of the nonlinear dielectric and ionic response of solvent environments within the framework of joint densityfunctional theory, with precisely the same optimizable parameters as conventional polarizable continuum models. We demonstrate that the resulting nonlinear theory agrees with the standard linear models for organic molecules and metallic surfaces under typical operating conditions. However, we find that the saturation effects in the rotational response of polar solvent molecules, inherent to our nonlinear theory, are crucial for a qualitatively correct description of the ionic surfaces typical of the solid electrolyte interface. arXiv:1301.6189v1 [cond-mat.mtrl-sci]

Density-functional theory (DFT) has revolutionized computational prediction of atomic-scale properties from first principles in physics, chemistry and materials science. Continuing development of new methods is necessary for accurate predictions of new classes of materials and properties, and for connecting to nano- and mesoscale properties using coarse-grained theories. JDFTx is a fully-featured open-source electronic DFT software designed specifically to facilitate rapid development of new theories, models and algorithms. Using an algebraic formulation as an abstraction layer, compact C++11 code automatically performs well on diverse hardware including GPUs (Graphics Processing Units). This code hosts the development of joint density-functional theory (JDFT) that combines electronic DFT with classical DFT and continuum models of liquids for first-principles calculations of solvated and electrochemical systems. In addition, the modular nature of the code makes it easy to extend and interface with, facilitating the development of multi-scale toolkits that connect to ab initio calculations, e.g. photo-excited carrier dynamics combining electron and phonon calculations with electromagnetic simulations.

Secondary batteries based on earth-abundant sodium metal anodes are desirable for both stationary and portable electrical energy storage. Room-temperature sodium metal batteries are impractical today because morphological instability during recharge drives rough, dendritic electrodeposition. Chemical instability of liquid electrolytes also leads to premature cell failure as a result of parasitic reactions with the anode. Here we use joint density-functional theoretical analysis to show that the surface diffusion barrier for sodium ion transport is a sensitive function of the chemistry of solid–electrolyte interphase. In particular, we find that a sodium bromide interphase presents an exceptionally low energy barrier to ion transport, comparable to that of metallic magnesium. We evaluate this prediction by means of electrochemical measurements and direct visualization studies. These experiments reveal an approximately three-fold reduction in activation energy for ion transport at a sodium bromide interphase. Direct visualization of sodium electrodeposition confirms large improvements in stability of sodium deposition at sodium bromide-rich interphases.

The integration of renewable, and often intermittent, energy sources such as solar and wind into the energy landscape, as well as the electrification of transportation, requires dramatic advances in electrical energy conversion and storage technologies including fuel cells, batteries and supercapacitors. TEM detection of lithium through a liquid is difficult, because lithium is a weak elastic scatterer and multiple scattering from the liquid overwhelms the inelastic core-loss signal in electron energy-loss spectroscopy (EELS). In this work, we successfully observed the lithiation state by valence energy-filtered TEM (EFTEM), which probes the low-energy regime (~1-10 eV), and allows us to work in thicker liquid layers than core-level A Baseline for Electrochemistry in the TEMWe use a liquid cell holder developed by Protochips using chips we designed to mimic a typical electrochemical cell (Figure 1a-b). The tip of the holder is a microfluidic flow cell with silicon nitride viewing membranes that confine a liquid, shown in cross section in Figure 1a. Figure 1b illustrates the top chip, with three patterned electrodes optimized for electrochemical cycling and imaging. Traditional silicon-processing methods use a chromium adhesion layer and gold electrodes. However, chromium diffuses rapidly 6 through gold (especially at grain boundaries) and can affect and even dominate the electrochemical signal. In addition, high-atomic-number electrodes such as Pt and Au obscure imaging. Instead, we used a carbon working electrode which only weakly scatters electrons and is commonly used in bulk electrochemistry, and titanium adhesion layers under platinum reference and counter electrodes. This allows us to image through the electrode with little loss in spatial resolution and contrast, which is dominated by scattering in the liquid instead. As a practical matter, and discussed below, spatial resolution is often limited by the low doses needed to control radiation damage than by beam spreading in the cell.To demonstrate that in situ electrochemistry reproduces well-established criteria, we performed cyclic voltammetry of a film of platinum, shown in Figure 1c-d, in the TEM.This control experiment represents a test case for quantitative electrochemistry, since the features are surface effects -including hydrogen adsorption and desorption and oxide formation and reduction -which are sensitive to contaminants at the sub-monolayer level.The in situ electrochemistry reproduced the characteristic voltametric profile of a polycrystalline platinum electrode at an appropriate current scale, regardless of the electron beam. In thin liquid layers, the ohmic drop in the solution becomes significant, as evidenced by the slanted curve in Figure 1d. This implies an inherent compromise between the highest spatial resolution imaging and quantitative electrochemistry.Accounting for ohmic drops in solution, this setup replicates results of a conventional electrochemical cell while obtaining nanometer resolution. 7Having established the electroch...

Rechargeable batteries based on metallic anodes are of interest for fundamental and application-focused studies of chemical and physical kinetics of liquids at solid interfaces. Approaches that allow facile creation of uniform coatings on these metals to prevent physical contact with liquid electrolytes, while enabling fast ion transport, are essential to address chemical instability of the anodes. Here, we report a simple electroless ion-exchange chemistry for creating coatings of indium on lithium. By means of joint density functional theory and interfacial characterization experiments, we show that In coatings stabilize Li by multiple processes, including exceptionally fast surface diffusion of lithium ions and high chemical resistance to liquid electrolytes. Indium coatings also undergo reversible alloying reactions with lithium ions, facilitating design of high-capacity hybrid In-Li anodes that use both alloying and plating approaches for charge storage. By means of direct visualization, we further show that the coatings enable remarkably compact and uniform electrodeposition. The resultant In-Li anodes are shown to exhibit minimal capacity fade in extended galvanostatic cycling when paired with commercial-grade cathodes.