Early Failure of Lithium-Sulfur Batteries at Practical Conditions: Crosstalk between Sulfur Cathode and Lithium Anode.

Lithium-sulfur (Li-S) batteries are one of the most promising next-generation energy storage technologies due to their high theoretical energy and low cost. However, Li-S cells with practically high energy still suffer from a very limited cycle life with reasons which remain unclear. Here, through cell study under practical conditions, it is proved that an internal short circuit (ISC) is a root cause of early cell failure and is ascribed to the crosstalk between the S cathode and Li anode. The cathode topography affects S reactions through influencing the local resistance and electrolyte distribution, particularly under lean electrolyte conditions. The inhomogeneous reactions of S cathodes are easily mirrored by the Li anodes, resulting in exaggerated localized Li plating/stripping, Li filament formation, and eventually cell ISC. Manipulating cathode topography is proven effective to extend the cell cycle life under practical conditions. The findings of this work shed new light on the electrode design for extending cycle life of high-energy Li-S cells, which are also applicable for other rechargeable Li or metal batteries.

Modeling the Cooperative Adsorption of Solid-Binding Proteins on Silica: Molecular Insights from Surface Plasmon Resonance Measurements.

Combinatorially selected solid-binding peptides (SBPs) provide a versatile route for synthesizing advanced materials and devices, especially when they are installed within structurally or functionally useful protein scaffolds. However, their promise has not been fully realized because we lack a predictive understanding of SBP-material interactions. Thermodynamic and kinetic binding parameters obtained by fitting quartz crystal microbalance and surface plasmon resonance (SPR) data with the Langmuir model whose assumptions are rarely satisfied provide limited information on underpinning molecular interactions. Using SPR, we show here that a technologically useful SBP called Car9 confers proteins to which is fused a sigmoidal adsorption behavior modulated by partner identity, quaternary structure, and ionic strength. We develop a two-step cooperative model that accurately captures the kinetics of silica binding and provides insights into how SBP-SBP interactions, fused scaffold, and solution conditions modulate adsorption. Because cooperative binding can be converted to Langmuir adhesion by mutagenesis, our approach offers a path to identify and to better understand and design practically useful SBPs.

Optimal charging profiles for mechanically constrained lithium-ion batteries.

The cost and safety related issues of lithium-ion batteries require intelligent charging profiles that can efficiently utilize the battery. This paper illustrates the application of dynamic optimization in obtaining the optimal current profile for charging a lithium-ion battery using a single-particle model while incorporating intercalation-induced stress generation. In this paper, we focus on the problem of maximizing the charge stored in a given time while restricting the development of stresses inside the particle. Conventional charging profiles for lithium-ion batteries (e.g., constant current followed by constant voltage) were not derived by considering capacity fade mechanisms. These charging profiles are not only inefficient in terms of lifetime usage of the batteries but are also slower since they do not exploit the changing dynamics of the system. Dynamic optimization based approaches have been used to derive optimal charging and discharging profiles with different objective functions. The progress made in understanding the capacity fade mechanisms has paved the way for inclusion of that knowledge in deriving optimal controls. While past efforts included thermal constraints, this paper for the first time presents strategies for optimally charging batteries by guaranteeing minimal mechanical damage to the electrode particles during intercalation. In addition, an executable form of the code has been developed and provided. This code can be used to identify optimal charging profiles for any material and design parameters.

Perturbation solution of the shape of a nonaxisymmetric sessile drop.

We develop an approximate analytical solution for the shape of a nonaxisymmetric sessile drop using regular perturbation methods and ignoring gravity. We assume that the pinned, contorted triple-line shape is known and is a small perturbation of the circular footprint of a spherical cap. We obtain an analytical solution using regular perturbation methods that we validate by comparing to the numerical solution of the Young-Laplace equation obtained using publicly available Surface Evolver software. In this process, we also show that the pressure inside the perturbed drop is unchanged and relate this to the curvature of the drop using the Young-Laplace equation. The rms error between the perturbation and Evolver solutions is calculated for a range of contact angles and amplitudes of triple-line perturbations. We show that the perturbation solution matches the numerical results well for a wide range of contact angles. In addition, we calculate the extent to which the drop surface is affected by triple-line contortions. We discuss the applicability of this solution to the possibility of real time hybrid experimental/computational characterization of the 3D sessile drop shapes, including obtaining local contact angle information.

Monte Carlo simulation of electrodeposition of copper: a multistep free energy calculation.

Electrodeposition of copper (Cu) involves length scales of a micrometer or even less. Several theoretical techniques such as continuum Monte Carlo, kinetic Monte Carlo (KMC), and molecular dynamics have been used for simulating this problem. However the multiphenomena characteristics of the problem pose a challenge for an efficient simulation algorithm. Traditional KMC methods are slow, especially when modeling surface diffusion with large number of particles and frequent particle jumps. Parameter estimation involving thousands of KMC runs is very time-consuming. Thus a less time-consuming and novel multistep continuum Monte Carlo simulation is carried out to evaluate the step wise free energy change in the process of electrochemical copper deposition. The procedure involves separate Monte Carlo codes employing different random number criterion (using hydrated radii, bare radii, hydration number of the species, redox potentials, etc.) to obtain the number of species (CuCl(2) or CuSO(4) or Cu as the case may be) and in turn the free energy. The effect of concentration of electrolyte, influence of electric field and presence of chloride ions on the free energy change for the processes is studied. The rate determining step for the process of electrodeposition of copper from CuCl(2) and CuSO(4) is also determined.