The practical applications of lithium–sulfur (Li–S) batteries are greatly hindered by the poor conductivity of sulfur, the shuttling of lithium polysulfides (LiPSs), and the sluggish kinetics in the charge–discharge process. In order to solve these problems, here we propose the surface-functionalized V₂N MXenes as the host materials to improve the electrochemical performance of Li–S batteries. Based on the density functional theory (DFT) calculations, we found that both the bare and functionalized V₂NT₂ (T = O, F, OH, and S) exhibit metallicity, and three of them (V₂NO₂, V₂NF₂, and V₂NS₂) possess moderate LiPS adsorption strength, which thermodynamically benefits the suppression of the dissolution and shuttling of LiPSs. Besides, V₂NS₂ shows the lowest Gibbs free energy barrier for the sulfur reduction reaction (0.49 eV) during discharge, which kinetically suppresses the dissolution and shuttling of LiPSs by expediting the decomposition process from soluble LiPSs to insoluble ones. Moreover, surface functionalized V₂NT₂ also exhibits outstanding catalytic ability for Li₂S decomposition during charge, which decreases the energy barrier from 3.64 eV (bare V₂N) to 1.55 (V₂NO₂) and 1.19 eV (V₂NS₂), and increases the charging kinetics. Based on these results, V₂NS₂ monolayers are suggested as promising host materials for S cathodes due to the fast charge/discharge kinetics and effective suppression of LiPS shuttling. This theoretical study provides further insight into the application of nitride MXenes and other two-dimensional materials as conductive anchoring materials for Li–S batteries.

中文翻译：

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氮化物 MXenes 作为硫主体用于多硫化物穿梭的热力学和动力学抑制：一项计算研究

锂硫（Li-S）电池的实际应用受到硫导电性差、多硫化锂（LiPSs）的穿梭以及充放电过程缓慢的动力学的极大阻碍。为了解决这些问题，我们提出表面功能化的 V ₂ N MXenes 作为主体材料，以提高 Li-S 电池的电化学性能。基于密度泛函理论 (DFT) 计算，我们发现裸露和功能化的 V ₂ NT ₂ (T = O、F、OH 和 S) 都表现出金属丰度，其中三个 (V ₂ NO ₂、V ₂ NF ₂和 V ₂ NS ₂) 具有中等的 LiPS 吸附强度，这在热力学上有利于抑制 LiPS 的溶解和穿梭。此外，V ₂ NS ₂在放电过程中表现出最低的硫还原反应的吉布斯自由能垒（0.49 eV），通过加速从可溶性LiPSs到不溶性LiPSs的分解过程，在动力学上抑制了LiPSs的溶解和穿梭。此外，表面功能化的 V ₂ NT ₂在充电过程中对 Li ₂ S 分解也表现出出色的催化能力，将能垒从 3.64 eV（裸 V ₂ N）降低到 1.55（V ₂ NO ₂）和 1.19 eV（V ₂NS ₂ )，并增加充电动力学。基于这些结果，由于快速充电/放电动力学和对 LiPS 穿梭的有效抑制，V ₂ NS ₂单层被认为是 S 正极的有前途的主体材料。该理论研究为氮化物 MXenes 和其他二维材料作为 Li-S 电池导电锚定材料的应用提供了进一步的见解。