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Plating in lithium-ion batteries not only reduces their lifetime, but also raises safety concerns. Preventing metallic lithium from forming is difficult, as the heterogeneity of materials typically used in batteries can create transport non-uniformities, which can lead to unanticipated local plating. Therefore, being able to predict the occurrence of plating due to a non-uniformity of a certain shape and size becomes essential. In this study, we probe the importance of the size scale and geometry on localized plating through numerical simulations and experiments. Using modified separators to create transport non-uniformities, we show that certain geometric features lead to more vulnerability to plating, and localization strongly depends on size. A single large feature in a separator induces more plating than a collection of smaller features with same total area. Our findings help elucidate the fundamentals behind heterogeneous plating, which can provide practical insights into battery safety and product control.

We use all-atom molecular dynamics simulations informed by density functional theory calculations to investigate aqueous ion transport across sub-nanoporous monolayer molybdenum disulfide (MoS 2 ) membranes subject to varying tensile strains. Driven by a transmembrane electric field, highly mechanosensitive permeation of both anions and cations is demonstrated in membranes featuring certain pore structures. For pores that are permeable when unstrained, we demonstrate ion current modulation by a factor of over 20 in the tensile strain range of 0 -4%. For unstrained pores that are impermeable, a clear strain-induced onset of permeability is demonstrated within the same range of strains. The underlying mechanism is shown to be a strain-induced reduction of the generally repulsive ion-pore interactions resulting from the ions' short-range interactions with the atoms in the pore interior and desolvation effects. The mechanosensitive pores considered in this work gain their electrostatic properties from the pore geometries and in principle do not require additional chemical functionalization. Here we propose the possibility of a new class of mechanosensitive nanoporous materials with permeation properties determined by the targeted engineering of vacancy defects.

The performance of electric double-layer capacitors is strongly influenced by the choice of electrolyte, and electrolytes comprised of ionic liquid mixtures have shown promise for enabling high energy densities. Here we perform all-atom molecular dynamics simulations of ionic liquids containing 1-ethyl-3methylimidazolium and different fractions of bis(trifluoromethylsulfonyl)imide and tetrafluoroborate, in conjunction with planar graphene sheets as electrodes. We demonstrate that relative ion−electrode van der Waals interactions play an important role in the population of ions adsorbed in the first interfacial layer near uncharged electrodes. Near charged electrodes, we find that the ionic liquid mixtures generally exhibit integral capacitances intermediate between the two pure ionic liquids. We characterize cumulative ion densities near electrodes carrying various surface charges, revealing different charging mechanisms for different ionic liquids, which we relate to the relative sizes of the ions. Finally, in the ionic liquid mixtures we identify an effective ion exchanging phenomenon wherein charging of the electrodes leads to different trends in the densities of the two types of anions in the first interfacial layer, which enhances counterion adsorption and improves capacitance at the negative electrode.

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