Lithium metal is an ideal anode for rechargeable lithium-battery technology. However, the extreme reactivity of Li metal with electrolytes leads to solid electrolyte interphase (SEI) layers that often impede Li+ transport across interfaces. The challenge is to predict the chemical, structural, and topographical heterogeneities of SEI layers arising from a multitude of interfacial constituents. Traditionally, the pathways and products of electrolyte decomposition processes were analyzed with the basic and simplifying presumption of an initial pristine Li-metal surface. However, ubiquitous inorganic passivation layers on Li metal can reduce electronic charge transfer to the electrolyte and significantly alter the SEI layer evolution. In this study, we analyzed the effect of nanometric Li2O, LiOH, and Li2CO3 as surface passivation layers on the interfacial reactivity of Li metal, using ab initio molecular dynamics (AIMD) calculations and X-ray photoelectron spectroscopy (XPS) measurements. These nanometric layers impede the electronic charge transfer to the electrolyte and thereby provide some degree of passivation (compared to pristine lithium metal) by altering the redox-based decomposition process. The Li2O, LiOH, and Li2CO3 layers admit varying levels of electron transfer from a Li-metal slab and subsequent storage of the electronic charges within their structures. As a result, their ability to transfer electrons to the electrolyte molecules, as well as the extent of decomposition of bis­(trifluoromethanesulfonyl)­imide anions, is significantly reduced compared to similar processes on pristine Li metal. The XPS experiments revealed that when Li2O is the major component on the altered surface, LiF phases formed to a greater extent. The presence of a dominant LiOH layer, however, results in enhanced sulfur decomposition processes. From AIMD studies, these observations can be explained based on the calculated quantities of electronic charge transfer found for each of the passivating films.

The lithium−sulfur battery is a promising next generation energy storage technology that could meet the demands of modern society with a theoretical specific energy near 2500 W h kg −1 . However, this battery chemistry faces unique problems such as the parasitic polysulfide shuttle reaction, which hinders battery performance severely. This shuttle phenomenon is caused by solubilities of intermediate reaction products in the electrolyte during the reduction chemistry of the battery. With molecular simulation and computational chemistry tools, we studied the thermodynamics, solvation structure, and dynamics of the long-chain lithium polysulfide species Li 2 S 6 and Li 2 S 8 in dimethoxyethane and 1,3-dioxolane to gain a deeper fundamental understanding of this process. We determined the structure of the first solvation shell for Li + as well as those of Li 2 S 6 , Li 2 S 8 closed, and Li 2 S 8 linear in pure solvents and solvents with extra Li + added. The lithium polysulfide species were found not to favor dissociation and would most likely exist as fully lithiated species in solution.

Lithium–sulfur batteries present a complex interconnected chemistry where the three componentsanode, electrolyte, and cathodestrongly interact with each other. One of the main issues associated with these interactions is the dissolution in the electrolyte solution of part of the sulfur reduction products (mainly long-chain polysulfides) during the discharge reactions at the cathode. These dissolved species can migrate and react at the anode surface producing undesired insulating films. A potential solution to mitigate this problem is to resort to additional materials which can act as anchors of the soluble species thus avoiding their migration. Density functional theory and ab initio molecular dynamics simulations are employed to investigate the ability of certain substrates to retain long-chain polysulfides (Li2S6 and Li2S8) at their surfaces in the presence of a pure solvent or a lithiated solution. Nanopores of graphene are first tested because the cathode is usually a mix of sulfur and carbon. Then, MoS2 and Mo-doped graphene are evaluated because of the well-known Mo–S affinity. Finally, a material which has been reported successful in experimental studies, MnO2, is analyzed and compared with another oxide surface, Fe2O3. Adsorption energies of the polysulfides to the surfaces and the detailed interactions of the Li ions and S atoms with the substrate are characterized via charge and geometric analyses. Both the Mo-containing materials and the oxides adsorb the polysulfides much more strongly than graphene nanopores do. However, some of these surfaces are found to be excessively reactive. A balance between affinity for S and moderate surface reactivity is found as a promising guideline for designing these materials.

Atomic layer deposition (ALD) is a surface synthesis technique that is characterized by self-limiting reactions between gas-phase precursors and a solid substrate. Although ALD processes have been demonstrated that span the periodic table, a greater understanding of the surface chemistry that affords ALD is necessary to enable greater precision, including area- and site-selective growth. We offer new insight into the thermodynamics and kinetics of the trimethylaluminum (TMA) and H2O ALD half-reactions with calibrated and time-resolved in situ pyroelectric calorimetry. The half-reactions produce 3.46 and 2.76 eV/Al heat, respectively, which is greater than the heat predicted by computational models based on crystalline Al2O3 substrates and closely aligned with the heat predicted by standard heats of formation. The pyroelectric thin-film calorimeter offers submillisecond temporal resolution that uniquely and clearly resolves precursor delivery and reaction kinetics. Both half-reactions are observed to exhibit multiple kinetic rates, with average TMA half-reaction rates at least 2 orders of magnitude faster than the H2O half-reaction kinetics. Comparing the experimental heat with published computational literature and additional first-principles modeling highlights the need to refine our models and mechanistic understanding of even the most ubiquitous ALD reactions.

The use of a lithium metal anode still presents a challenging chemistry and engineering problem that holds back next generation lithium battery technology. One of the issues facing lithium metal is the presence of the solid electrolyte interphase (SEI) layer that forms on the electrode creating a variety of chemical species that change the properties of the electrode and is closely related to the formation and growth of lithium dendrites. In order to advance the scientific progress of lithium metal more must be understood about the fundamentals of the SEI. One property of the SEI that is particularly critical is the passivating behavior of the different SEI components. This property is critical to the continued formation of SEI and stability of the electrolyte and electrode. Here we report the investigation of the passivation behavior of Li2O, Li2CO3, LiF and LiOH with the lithium salt LiFSI. We used large computational chemistry models that are able to capture the lithium/SEI interface as well as the SEI/electrolyte interface. We determined that LiF and Li2CO3 are the most passivating of the SEI layers, followed by LiOH and Li2O. These results match previous studies of other Li salts and provide further examination of LiFSI reduction.