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Due to the low sulfur utilization, slow battery kinetics, and shuttle effect of lithium polysulfides (LiPSs), the practical application of lithium−sulfur (Li−S) batteries is severely limited. Understanding the reaction mechanism is very important for the design and application of high-performance batteries. Herein, the adsorption mechanism of LiPSs, the reaction mechanism of a battery electrode, and the catalytic decomposition of LiPSs on pristine, single-atom, and dual-atom doping C 9 N 4 (C 9 N 4 , M/C 9 N 4 , and M 1 −M 2 /C 9 N 4 ) nanosheets are comprehensively considered for the first time. Through bond length analysis, charge analysis, and energy analysis, the doping of metal atoms, especially co-doping of V and Zn atoms (Zn−V/C 9 N 4 ), can greatly improve the adsorption performance of material C 9 N 4 . More importantly, Zn−V/C 9 N 4 can significantly reduce the reaction energy barrier of the battery electrode (0.144 eV) and the decomposition energy barrier of Li 2 S (0.661 eV). The simulation results show that high catalytic activity depends on the unique dorbital coupling and the ″pull″ effect of metal co-doping. These findings are crucial to understanding the role of dual-atom doping carbon materials in the design of cathode materials to cope with the performance constraints in lithium−sulfur batteries. We hope that this research idea can also be applied to other dual-atom systems.

Formation damage evaluation is a key and basic link in optimizing working fluids. It is widely accepted that formation damage is the reduction of core plugs permeability caused by working fluid invasion. However, the measurement of permeability faces a huge challenge for shale formation, such as overspending, time-consuming and the scarcity of unbroken core plug samples. A new method of fractal analysis derived from Scanning Electron Microscopy (SEM) image of shale pore structure was used to quantify the shale formation damage. This method needs to select optimal magnification and segmentation threshold value of SEM image to obtain exact Fractal Dimension (FD) of pore structure. In this paper, we take the black shale outcrops from Sichuan Basin for an example. The results shows that the optimal magnification for observation of the pore structure using SEM imaging in this area is 1000×, and the optimal threshold value for binary image is 29 (RGB). Microscopic pore structure of the shale follows the fractal law, and the FDs increase with increasing measurement scales. It is evident that the evaluation results of shale formation damage when exposed to 2 wt.% NaOH solution and 2 wt.% brine solution using microstructure fractal are exceptionally in good agreement with permeability reduction results. The microstructure fractal obtained from SEM images provides a new method for evaluation of shale formation damage. And it can be applied to optimize the screening working fluids used in shale formation in real time under the condition of high temperature and high pressure.

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