Electrolyte Dependence of Li Transport Mechanisms in Small Molecule Solvents from Classical Molecular Dynamics.

As demands on Li-ion battery performance increase, the need for electrolytes with high ionic conductivity and a high Li transference number () becomes crucial to boost power density. Unfortunately, in liquid electrolytes is typically <0.5 due to Li migrating via a vehicular mechanism, whereby Li diffuses along with its solvation shell, making its diffusivity slower than the counteranion.

Accelerating amorphous polymer electrolyte screening by learning to reduce errors in molecular dynamics simulated properties.

Polymer electrolytes are promising candidates for the next generation lithium-ion battery technology. Large scale screening of polymer electrolytes is hindered by the significant cost of molecular dynamics (MD) simulation in amorphous systems: the amorphous structure of polymers requires multiple, repeated sampling to reduce noise and the slow relaxation requires long simulation time for convergence. Here, we accelerate the screening with a multi-task graph neural network that learns from a large amount of noisy, unconverged, short MD data and a small number of converged, long MD data.

Tunable Redox Mediators for Li-O Batteries Based on Interhalide Complexes.

Li-O batteries can provide significantly higher gravimetric energy density than Li-ion batteries, but their practical use is limited by a number of fundamental issues associated with oxidizing discharge products such as LiO and LiOH during charging. Soluble inorganic redox mediators (RMs) like LiI and LiBr have been shown to enhance round-trip efficiency where different solvents can greatly shift the redox potential of the RMs, significantly altering the overpotential during charging, as well as their oxidizing power against the discharge product. Unfortunately, other design requirements like (electro)chemical stability with the electrode as well as reactive discharge products greatly constrain the selection of solvent, making it impractical to additionally design the solvent to provide optimal RM performance.

Importance of Equilibration Method and Sampling for Molecular Dynamics Simulations of Solvent-Lithium-Salt Systems in Lithium-Oxygen Batteries.

We examine the effect of equilibration methodology and sampling on molecular dynamics (AIMD) simulations of systems of common solvents and salts found in lithium-oxygen batteries. We compare two equilibration methods: (1) using an AIMD temperature ramp and (2) using a classical MD simulation followed by a short AIMD simulation both at the target simulation temperature of 300 K. We also compare two different classical all-atom force fields: PCFF+ and OPLS.

Quantitative Mapping of Molecular Substituents to Macroscopic Properties Enables Predictive Design of Oligoethylene Glycol-Based Lithium Electrolytes.

Molecular details often dictate the macroscopic properties of materials, yet due to their vastly different length scales, relationships between molecular structure and bulk properties can be difficult to predict , requiring Edisonian optimizations and preventing rational design. Here, we introduce an easy-to-execute strategy based on linear free energy relationships (LFERs) that enables quantitative correlation and prediction of how molecular modifications, i.e.

Supramolecular Regulation of Anions Enhances Conductivity and Transference Number of Lithium in Liquid Electrolytes.

Achieving high ionic conductivity in lithium-ion battery (LIB) electrolytes requires dissociation of Li-salts; however, though the generation of free Li from salt dissociation is advantageous, the presence of freely diffusing anions may reduce the Li transference number. The use of supramolecular anion recognition to regulate and modify ion-pairing and diffusion of anions in battery electrolytes is yet to be deeply understood. Herein, we demonstrate that addition of a selective and strong PF-binding macrocycle to a solution of LiPF in low dielectric media leads to enhanced ion pair dissociation and an increased Li transference number.

Using entropy measures to characterize human locomotion.

Entropy measures have been widely used to quantify the complexity of theoretical and experimental dynamical systems. In this paper, the value of using entropy measures to characterize human locomotion is demonstrated based on their construct validity, predictive validity in a simple model of human walking and convergent validity in an experimental study. Results show that four of the five considered entropy measures increase meaningfully with the increased probability of falling in a simple passive bipedal walker model.