An organotetrasulfide consists of a linear chain of four sulfur atoms that could accept up to 6 e in reduction reactions, thus providing a promising high-capacity electrode material. Herein, we study three bis(aryl) tetrasulfides as cathode materials in lithium batteries. Each tetrasulfide exhibits two major voltage regions in the discharge. The high voltage slope region is governed by the formation of persulfides and thiolates, and the low voltage plateau region is due to the formation of Li S /Li S. Based on theoretical calculations and spectroscopic analysis, three reduction reaction processes are revealed, and the discharge products are identified. Lithium half cells with tetrasulfide catholytes deliver high specific capacities over 200 cycles. The effects of the functional groups on the electrochemical characteristics of tetrasulfides are investigated, which provides guidance for developing optimum aryl polysulfides as cathode materials for high energy lithium batteries.

Lithium−sulfur (Li−S) batteries are a promising alternative to the Li-ion technology due to their high theoretical capacity and low cost. Unlike intercalation compounds, the sulfur cathode undergoes a series of complex electrochemical reactions that give rise to substantial structural and morphological changes. Here, we report ab initio molecular dynamics simulations of the lithiation and delithiation reactions that are important in Li−S batteries. The lithiation is studied on two low-energy surfaces, (100) and ( 001), of sulfur (S 8 ), whereas delithiation is studied on the (111) surface of lithium sulfide (Li 2 S). The effect of electrolyte is included by constructing interfacial systems between these surfaces and dimethoxyethane, a widely used liquid electrolyte. During both lithiation and delithiation, a layerby-layer reaction pattern is revealed. The evolution of atomistic structure and reaction voltage during lithiation and delithiation is studied, and the microscopic reaction mechanisms are analyzed. Dissolution of lithium polysulfides into the electrolyte is also observed in our simulations, which is attributed to the strong interaction between lithium polysulfides and electrolyte molecules in the form of lithium bonds. Studies of the delithiation process in Li 2 S confirm that the experimentally observed initial charge barrier is of kinetic origin.

A bis(aryl) tetrasulfide consists of a linear chain of four sulfur atoms that could accept up to 6 Li in reduction reactions, thus providing a promising high‐capacity cathode material for rechargeable lithium batteries. Here, three bis(aryl) tetrasulfides with different functional groups have been investigated and the effects of the functional group X (OCH3, H, or CF3) on the properties and electrochemical characteristics of aryl tetrasulfides are summarized. For more information, see the Communication by Y. Fu et al. on page 16941 ff.

Lithium ion batteries are among the most widely used energy storage devices in consumer electronics. However, limited capacity is still a major problem that hinders their application in a few key markets including electric vehicles. Many different materials are currently under intensive investigation, and lithium sulfide (Li2S) is a promising high capacity cathode material with a theoretical capacity of 1,166 mAh/g that is almost four times higher than what is offered by current commercially available cathodes. The Li2S cathode is also attractive since it can be used with a lithium metal free anode. Unfortunately, the delithiation of Li2S is usually sluggish, and a high charge voltage is required as a result. To understand the associated microscopic mechanism of the delithiation process in Li2S, first principles calculations based on the density function theory are performed using the Vienna Ab initio Simulation Package (VASP). A few low energy Li2S surfaces are created, and the delithiation processes on these surfaces are simulated by extracting a lithium ion on the surface. The resulting energy barriers are recorded and compared, and it is found that different surfaces lead to very different diffusion barriers, suggesting a possible route to minimize the diffusion barrier through the control of the equilibrium shape of the Li2S particles. The structural evolutions for systems with different amount of lithium vacancies that correspond to different percent of delithiation are simulated using ab initio molecular dynamics. To study the possible effects of the electrolyte, these simulations are also performed in the presence of electrolyte. The equilibrium structure of the electrolyte is first determined by ab initio molecular dynamics using a melt-quench process. The Li2S/electrolyte interfaces are then formed and the diffusion barriers are calculated. Three different electrolytes are studied and compared. These calculations provide an atomistic understanding of the delithiation process in Li2S, and help to develop new methods that can be used to minimize the activation barrier of Li2S particles.