Two-dimensional (2D) carbon allotropes have attracted great attention in both science and engineering fields. Their extraordinary and/or unique properties make them promising for engineering applications, ranging from metal-ion batteries to biosensors. Herein, by employing first-principles calculations, we propose a new 2D planar carbon allotrope, popgraphene, which is composed of 5–8–5 carbon rings. Using a bottom-up approach, popgraphene could be constructed via the formation of atomically precise 5–8–5 line defects in graphene by simultaneous electron irradiation. Popgraphene is intrinsically metallic. It has low energy and possesses great dynamic, thermal and mechanical stability. Our calculations also show that it has a high theoretical capacity for Li atoms (Li₄C₆: 1487 mA h g⁻¹), a low Li diffusion barrier (<0.55 eV), and a low average open circuit voltage (0.45 V). Such excellent characteristics suggest that programmable metallic popgraphene is a promising anode material for use in Li-ion batteries (LIBs) with fast charge/discharge rates. Our simulation results also indicate that van der Waals corrections play little role in the structural parameters of popgraphene, whereas they play a central role in the adsorption and diffusion abilities as well as the electrochemical performance of popgraphene. This study provides fundamental insight into the design of new materials with extraordinary properties for their excellent applications, including for the next generation of LIBs, and may open up a cutting-edge field in programming experimentally realized low-dimensional materials.

The structure of hydrated ions plays a central role in chemical and biological sciences. In the present paper, five ions, namely, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Cl^–, are examined using molecular dynamics simulations. In addition to hydrated individual ions and ion pairs identified previously, hydrated ion clusters containing 3, 4, 5, or more ions are identified in the present paper. The dependence of hydration numbers and mole fractions of individual ions, ion pairs, and larger ion clusters on the electrolyte concentration is determined. As the electrolyte concentration increases, the mole fraction of hydrated individual ions decreases, and the mole fraction of hydrated larger ion clusters increases. The results also reveal that the hydrogen bonding numbers of the H₂O molecules of the first hydration shells of individual ions, ion pairs, and larger ion clusters are insensitive to the electrolyte concentration, but sensitive to the nature and conformation of ions.

Exploring new materials and methods to achieve high utilization of sulfur with lean electrolyte is still a common concern in lithium‐sulfur batteries. Here, high‐density oxygen doping chemistry is introduced for making highly conducting, chemically stable sulfides with a much higher affinity to lithium polysulfides. It is found that doping large amounts of oxygen into NiCo₂S₄ is feasible and can make it outperform the pristine oxides and natively oxidized sulfides. Taking the advantages of high conductivity, chemical stability, the introduced large Li–O interactions, and activated Co (Ni) facets for catalyzing S_n^2–, the NiCo₂(O–S)₄ is able to accelerate the Li₂S‐S₈ redox kinetics. Specifically, lithium‐sulfur batteries using free‐standing NiCo₂(O–S)₄ paper and interlayer exhibit the highest capacity of 8.68 mAh cm^–2 at 1.0 mA cm^–2 even with a sulfur loading of 8.75 mg cm^–2 and lean electrolyte of 3.8 µL g^–1. The high‐density oxygen doping chemistry can be also applied to other metal compounds, suggesting a potential way for developing more powerful catalysts towards high performance of Li–S batteries.

Tunable thermal transport and mechanical properties of graphyne heterojunctions.