Polysulfide binding and trapping to prevent dissolution into the electrolyte by a variety of materials has been well studied in Li−S batteries. Here we discover that some of those materials can play an important role as an activation catalyst to facilitate oxidation of the discharge product, Li 2 S, back to the charge product, sulfur. Combining theoretical calculations and experimental design, we select a series of metal sulfides as a model system to identify the key parameters in determining the energy barrier for Li 2 S oxidation and polysulfide adsorption. We demonstrate that the Li 2 S decomposition energy barrier is associated with the binding between isolated Li ions and the sulfur in sulfides; this is the main reason that sulfide materials can induce lower overpotential compared with commonly used carbon materials. Fundamental understanding of this reaction process is a crucial step toward rational design and screening of materials to achieve high reversible capacity and long cycle life in Li−S batteries. T he ever-increasing demand for energy storage devices with high energy density, low material cost, and long cycle life has driven the development of new battery systems beyond the currently dominant lithium ion batteries (LIBs) (1). Among alternative battery chemistries, lithium−sulfur (Li−S) batteries have attracted remarkable attention due to their high theoretical energy density of 2,600 watt hours per kilogram, 5 times higher than those of state-of-the-art LIBs (2-4). In addition, sulfur, as a byproduct of the petroleum refining process, is naturally abundant, inexpensive, and environmentally friendly (5). However, the practical application of Li−S batteries is still plagued with numerous challenges. For example, the insulating nature of sulfur and discharge products Li 2 S/Li 2 S 2 leads to low active material utilization. In addition, the easy dissolution of lithium polysulfides (LiPSs) into the electrolyte causes LiPSs shuttling between cathode and anode and uncontrollable deposition of sulfide species on the lithium metal anode, inducing fast capacity fading and low coulombic efficiency (2, 6).Tremendous efforts have been taken to circumvent these concerns, with the nanostructuring of electrodes as one of the most effective approaches to overcoming the issues facing highcapacity electrode materials (2, 7). For example, the integration of nanostructured carbon materials with sulfur is one of the primary strategies for improving the electrical conductivity of the composites and suppression of polysulfide shuttling through physical confinement (8-14). However, it was first recognized by Zheng et al. (11) that the weak interaction between nonpolar carbon-based materials and polar LiPSs/Li 2 S species leads to weak confinement and easy detachment of LiPSs from the carbon surface, with further diffusion into the electrolyte causing capacity decay and poor rate performance. Therefore, the introduction of heteroatoms into carbonaceous materials (such as nitrogen, oxygen, boron, phosphorous, sulfur, or ...

batteries based on Li (Na) metal as the anode material, such as Li (Na)-S and Li (Na)-O 2 batteries. [6][7][8][9][10] The specific capacities of lithium and sodium metal can be up to 3860 and 1166 mA h g −1 , respectively, much higher than that of the graphite (372 mA h g −1 ) in the traditional Li-ion batteries (LIB) and also higher than that of zinc, lead, and cadmium. [3,11,12] Therefore, Li (Na) metal can be viewed as a promising anode material candidate for the next-generation secondary batteries. Unfortunately, commercialization of the secondary Li (Na) metal battery still faces many challenges, including the volumetric change of Li (Na) metal during charging and the complex physical and chemical reactions at the interface between Li (Na) metal and electrolyte, resulting in low Coulombic efficiency and growth of dendrites. [13][14][15][16] As a result, it is critical to search for the suitable protective films (PFs) with high ionic conductivity and excellent mechanical performance, in order to improve the electrochemical properties and suppress dendrite formation.Many strategies have been carried out to modify the nanoscale interphase between Li (Na) metal anode and electrolyte for improving performance of Li (Na) metal anode. Moreover, various kinds of external protection methods have developed including, inorganic or organic molecules coating, all-solid-state Rechargeable batteries based on lithium (sodium) metal anodes have been attracting increasing attention due to their high capacity and energy density, but the implementation of lithium (sodium) metal anode still faces many challenges, such as low Coulombic efficiency and dendrites growth. Layered materials have been used experimentally as protective films (PFs) to address these issues. In this work, the authors explore using first-principles computations the key factors that determine the properties and feasibility of various 2D layered PFs, including the defect pattern, crystalline structure, bond length, and metal proximity effect, and perform the simulations on both aspects of Li + (Na + ) ion diffusion property and mechanical stability. It is found that the introduction of defect, the increase in bond length, and the proximity effect by metal can accelerate the transfer of Li + (Na + ) ion and improve the ionic conductivity, but all of them make negative influences on the stiffness of materials against the suppression of dendrite growth and weaken both critical strains and critical stress. The results provide new insight into the interaction mechanism between Li + (Na + ) ions and PF materials at the atomic level and shed light onto exploring a variety of layered PF materials in metal anode battery systems.

Efficient flexible energy storage systems have received tremendous attention due to their enormous potential applications in self-powering portable electronic devices, including roll-up displays, electronic paper, and "smart" garments outfitted with piezoelectric patches to harvest energy from body movement. Unfortunately, the further development of these technologies faces great challenges due to a lack of ideal electrode materials with the right electrochemical behavior and mechanical properties. MXenes, which exhibit outstanding mechanical properties, hydrophilic surfaces, and high conductivities, have been identified as promising electrode material candidates. In this work, taking 2D transition metal carbides (TMCs) as representatives, we systematically explored several influencing factors, including transition metal species, layer thickness, functional group, and strain on their mechanical properties (e.g., stiffness, flexibility, and strength) and their electrochemical properties (e.g., ionic mobility, equilibrium voltage, and theoretical capacity). Considering potential charge-transfer polarization, we employed a charged electrode model to simulate ionic mobility and found that ionic mobility has a unique dependence on the surface atomic configuration influenced by bond length, valence electron number, functional groups, and strain. Under multiaxial loadings, electrical conductivity, high ionic mobility, low equilibrium voltage with good stability, excellent flexibility, and high theoretical capacity indicate that the bare 2D TMCs have potential to be ideal flexible anode materials, whereas the surface functionalization degrades the transport mobility and increases the equilibrium voltage due to bonding between the nonmetals and Li. These results provide valuable insights for experimental explorations of flexible anode candidates based on 2D TMCs.

Chemical-looping combustion is a promising technology with no contact between fuel and combustion air, featuring the inherent separation of CO 2 and avoidance of nitrogen oxide formation. To some metal oxide oxygen carriers, the high costs and positive hazard to living environment inhibit the application of chemicallooping combustion systems in large scale. In this work, we investigate the possibility of using calcium sulfate as oxygen carrier. The release amount of SO 2 was not only due to the reacting temperature but also affected by the partial pressure of CO in the reaction. If the partial pressure of CO in the atmosphere is big enough, the release amount of SO 2 or the occurrence of side reactions can be eliminated fully even if the temperature is as high as 1000 °C. The reactivity behavior of the reduction of CaSO 4 by CO in the heating process is also studied. The values of activation energy, frequency factor, and linear factor corresponding to five different heating rates are calculated using an accurate kinetics integral expression and a temperature integral approximation with high precision. The most probable mechanism function in the decomposition process is characterized by G(R) ) [-ln(1 -R)] 1/2 .

Chemical-looping combustion (CLC) is a promising technology to combine the energy-use situation in China and CO 2 zero emission in situ, which allows for CO 2 sequestration by efficient ways and without nitrogen oxide (NO x ) formation. An oxygen carrier with good performance is one of the key issues of the CLC process. Calcium sulfate has proven to be a kind of new oxygen carrier with sufficient reactivities in reduction and oxidation reactions, with enough ability for carrying oxygen and no secondary pollution. The decomposition mechanism of calcium sulfate with an average particle size of 8.934 µm in a different simulated atmosphere in CLC is investigated using a simultaneous thermal analyzer at five different heating rates. In an inert atmosphere, the relationship between activation energy and conversion fraction of calcium sulfate is obtained without the introduction of the reaction mechanism function. The values of activation energy, frequency factor, and linear factor corresponding to 5 different heating rates and 30 different common reaction mechanism functions, respectively, are calculated using an accurate kinetics integral expression and a temperature integral approximation with high precision. Kinetic parameters of the decomposition reaction without any disturbance of other reactions, including E βf0 and ln A βf0 , are determined by extrapolating the heating rate to zero. Additionally, the relationship between the activation energy of decomposition and conversion rate is found using the double-extrapolated method. The activation energy at the start of the decomposition reaction, E Rf0 , is also evaluated by extrapolating the conversion rate to zero. Whe E βf0 and E Rf0 are compared, the most likely mechanism function in the decomposition process is characterized by the Avrami-Erofeev equation and the reaction is dominated by the nucleation rate. The Avrami-Erofeev equation is also evaluated on the basis of the most likely mechanism function by the Popescu method.