Lithium-sulfur (Li-S) batteries mainly rely on the reversible electrochemical reaction of between lithium ions (Li⁺) and sulfur species to achieve energy storage and conversion, therefore, increasing the number of free Li⁺ and improving the Li⁺ diffusion kinetics will effectively enhance the cell performance. Here, Mo-based MXene heterostructure (MoS₂@Mo₂C) was developed by partial vulcanization of Mo₂C MXene, in which the introduction of similar valence S into Mo-based MXene (Mo₂C) can create an electron delocalization effect. Through theoretical simulations and electrochemical characterisation, it is demonstrated that the MoS₂@Mo₂C heterojunction can effectively promote ion desolvation, increase the amount of free Li⁺, and accelerate Li⁺ transport for more efficient polysulfide conversion. In addition, the MoS₂@Mo₂C material is also capable of accelerating the oxidation and reduction of polysulfides through its sufficient defects and vacancies to further enhance the catalytic efficiency. Consequently, the Li-S battery with the designed MoS₂@Mo₂C electrocatalyst performed for 500 cycles at 1 C and still maintained the ideal capacity (664.7 mAh·g⁻¹), and excellent rate performance (567.6 mAh·g⁻¹ at 5 C). Under the extreme conditions of high loading, the cell maintained an excellent capacity of 775.6 mAh·g⁻¹ after 100 cycles. It also retained 838.4 mAh·g⁻¹ for 70 cycles at a low temperature of 0 °C, and demonstrated a low decay rate (0.063%). These results indicate that the delocalized electrons effectively accelerate the catalytic conversion of lithium polysulfide, which is more practical for enhancing the behaviour of Li-S batteries.

Individual magnetic Fe₃O₄ nanoparticles were imaged using the developed frequency-modulated magnetic force microscopy (FM-MFM) technique. High-resolution imaging of ac magnetic field from individual magnetic nanoparticles was demonstrated by FM-MFM with a high-coercivity FePt tip. It was found that the amplitude and phase images of ac magnetic field were obtained separately using the technique with a lock-in amplifier. The distribution of magnetic field gradient of the individual nanoparticles is clearly presented. It was observed that magnetic nanoparticles can be more precisely detected by FM-MFM. The results are significant for study of the real magnetic field distribution of individual magnetic nanoparticles (~20 nm), which provide some valuable information for the analysis of nanoscale magnetic features.

There is no analytical solution to the stress, strain and displacement changes in the inner sleeve of the downhole packer during service. In this paper, the inner sleeve structure is simplified based on the shell theory model, and the geometric equation and physical equation suitable for the inner-sleeve structure are established based on the control differential equation of the cylindrical shell derived by Flügge. Finally, the analytical solution calculation program of the radial displacement, and strain and stress value of each node of the cylindrical shell under the external load condition is compiled by using MATLAB R2024a software. The analytical solution is compared with the numerical solution of each parameter under the same conditions, and the root mean square error between the numerical solution and the analytical solution is evaluated. The results show that the analytical formulas of the stress, strain and displacement of the inner sleeve structure of the downhole packer established in this paper can accurately obtain the above parameters. The root mean square errors between the analytical formulas and the numerical solutions are 0.083, 0.074 and 0.086, indicating that the fitting degree between the two is good, which verifies the effectiveness of the theoretical model based on the shell to describe the stress state of the inner sleeve. The model also accurately reflects the partial stress and strain law of the inner sleeve of the downhole packer to a certain extent. This study provides theoretical support for the design optimization of the inner sleeve of a pipeline packer, and also provides some guidance for the study of the stress state of its inner sleeve.