MoS2 nanosheets grown on hollow carbon spheres as a strong polysulfide anchor for high performance lithium sulfur batteries

In-situ decoration of tin sulfide on Niobium carbide MXene with robust electronic coupling for improved sodium storage performance

Tin sulfide (SnS) has been considered as one of the most promising sodium storage materials because of its excellent electrochemical activity, low cost, and low-dimensional structure. However, owing to the serious volume change upon discharging/charging and poor electronic conductivity, the SnS-based electrodes often suffer from electrode pulverization and sluggish reaction kinetics, thus resulting in serious capacity fading and degraded rate capability. In this work, SnS nanoparticles uniformly distributed on the surface of the layered Niobium carbide MXene (SnS/Nb₂CT_x) were fabricated through a facile solvothermal approach followed by calcination, endowing the SnS/Nb₂CT_x with a three-dimensional interconnected framework as well as fast charge transfer. Benefitting from the excellent electronic/ionic conductivity, efficient buffering matrix, abundant active sites, and high sodium storage activity inherited from the structure design, the robust electronic coupling between SnS nanoparticle and Nb₂CT_x MXene results in excellent electrochemical output, which demonstrates superior reversible capacities of 479.6 (0.1 A/g up to 100 cycles) and 278.9 mAh/g (0.5 A/g up to 500 cycles) upon sodium storage, respectively. The excellent electrochemical performance manifests the promise of the combination of metal sulfides with Nb₂CT_x MXene to fabricate high-performance electrodes for sodium storage.

Metal Ion Cutting-Assisted Synthesis of Defect-Rich MoS2 Nanosheets for High-Rate and Ultrastable Li2S Catalytic Deposition

Active metal ions often show a strong cutting effect on the chemical bonds during high-temperature thermal processes. Herein, a one-pot metal ion cutting-assisted method was adopted to design defect-rich MoS_2-x nanosheet (NS)/ZnS nanoparticle (NP) heterojunction composites on carbon nanofiber skeletons (CNF@MoS_2-x/ZnS) via a simple Ar-ambience annealing. Results show that Zn²⁺ ions capture S^2- ions from MoS₂ and form into ZnS NPs, and the MoS₂ NSs lose S^2- ions and become MoS_2-x ones. As sulfur hosts for lithium-sulfur batteries (LSBs), the CNF@MoS_2-x/ZnS-S cathodes deliver a high reversible capacity of 1233 mA h g^-1 at 0.1 C and keep 944 mA h g^-1 at 3 C. Moreover, the cathodes also show an extremely low decay rate of 0.012% for 900 cycles at 2 C. Series of analysis indicate that the MoS_2-x NSs significantly improve the chemisorption and catalyze the kinetic process of redox reactions of lithium polysulfides, and the heterojunctions between MoS_2-x NSs and ZnS NPs further accelerate the transport of electrons and the diffusion of Li⁺ ions. Besides, the CNF@MoS_2-x/ZnS-S LSBs also show an ultralow self-discharge rate of 1.1% in voltage. This research would give some new insights for the design of defect-rich electrode materials for high-performance energy storage devices.

A conductive framework embedded with cobalt-doped vanadium nitride as an efficient polysulfide adsorber and convertor for advanced lithium-sulfur batteries

The industrialization and commercialization of Li-S batteries are greatly hindered by several defects such as the sluggish reaction kinetics, polysulfide shuttling and large volume expansion. Herein, we propose a heteroatom doping method to optimize the electronic structure for enhancing the adsorption and catalytic activity of VN that is in situ embedded into a spongy N-doped conductive framework, thus obtaining a Co-VN/NC multifunctional catalyst as an ideal sulfur host. The synthesized composite has both the unique structural advantages and the synergistic effect of cobalt, VN, and nitrogen-doped carbon (NC), which not only improve the polysulfide anchoring of the sulfur cathode but also boost the kinetics of polysulfide conversion. The density functional theory (DFT) calculations revealed that Co doping could enrich the d orbit electrons of VN for elevating the d band center, which improves its interaction with lithium polysulfides (LiPSs) and accelerates the interfacial electron transfer, simultaneously. As a result, the batteries present a high initial discharge capacity of 1521 mA h g^-1 at 0.1 C, good rate performance, and excellent cycling performances (∼876 mA h g^-1 at 0.5 C after 300 cycles and ∼490 mA h g^-1 at 2 C after 1000 cycles, respectively), even with a high areal sulfur loading of 4.83 mg cm^-2 (∼4.70 mA h cm^-2 at 0.2 C after 100 cycles). This well-designed work provides a good strategy to develop effective polysulfide catalysis and further obtain high-performance host materials for Li-S batteries.

Machine-Learning-Enabled Tricks of the Trade for Rapid Host Material Discovery in Li-S Battery

The shuttle effect has been a major obstacle to the development of lithium-sulfur batteries. The discovery of new host materials is essential, but lengthy and complex experimental studies are inefficient for the identification of potential host materials. We proposed a machine learning method for the rapid discovery of an AB₂-type sulfur host material to suppress the shuttle effect using the 2DMatPedia database, discovering 14 new structures (PdN₂, TaS₂, PtN₂, TaSe₂, AgCl₂, NbSe₂, TaTe₂, AgF₂, NiN₂, AuS₂, TmI₂, NbTe₂, NiBi₂, and AuBr₂) from 1320 AB₂-type compounds. These structures have strong adsorptions of greater than 1.0 eV for lithium polysulfides and appreciable electron-transportation capability, which can serve as the most promising AB₂-type host materials in lithium-sulfur batteries. On the basis of a small data set, we successfully predicted Li₂S₆ adsorption at arbitrary sites on substrate materials using transfer learning, with a considerably low mean absolute error (below 0.05 eV). The proposed data-driven method, as accurate as density functional theory calculations, significantly shortens the research cycle of screening AB₂-type sulfur host materials by approximately 8 years. This method provides high-precision and expeditious solutions for other high-throughput calculations and material screenings based on adsorption energy predictions.

Fast polysulfide catalytic conversion and self-repairing ability for high loading lithium-sulfur batteries using a permselective coating layer modified separator

Li-S batteries are considered as one of the most promising battery systems because of their large theoretical capacity and high energy density. However, the "shuttle effect" of soluble polysulfides and sluggish electrochemical redox kinetics of Li-S batteries could cause a broken electrode structure and poor electrochemical performance. Herein, a high-performance and stable Li-S battery has been demonstrated by employing organo-polysulfide chain modified acetylene black (ABPS) as the coating layer on the separator. In addition to the traditional advantages of fast electron transport and polysulfide-interception ability of the carbon coating layer, the grafted organo-polysulfide chain endows the ABPS coating layer with permselectivity for lithium ion against polysulfides, electrocatalytic ability for the sluggish redox kinetics and self-repairing ability for the broken electrode. Hence, the battery prepared using an ABPS-coated separator delivers the best cycling performance (970 mA h g^-1 at 0.2 C after 100 cycles) and rate performance (805 mA h g^-1 at 2 C) as compared to the cells using acetylene black (AB)-coated or Celgard separators. Moreover, the Li-S battery prepared using an ABPS-coated separator exhibits a stable cycling performance at 1 C over 500 cycles with a low degradation of 0.04% per cycle, and a high coulombic efficiency (near 100%). Furthermore, as the sulfur loading was increased to 6.8 mg cm^-2, the Li-S battery using the ABPS-coated separator still could deliver a high areal capacity of 6.03 mA h cm^-2 with a low electrolyte/sulfur ratio (E/S = 4, μL_electrolyte mg_S^-1) after 170 cycles. Significantly, ABPS is an effective coating layer material for improving and stabilizing Li-S batteries.

Molybdenum disulfide nanosheets vertically grown on self-supported titanium dioxide/nitrogen-doped carbon nanofiber film for effective hydrogen peroxide decomposition and "memory catalysis"

A self-supporting catalyst consisting of 1D/2D vertical molybdenum disulfide@titanium dioxide/nitrogen-doped carbon nanofiber (MoS₂@TiO₂/NCNFs) was prepared and tested. It showed efficient hydrogen peroxide (H₂O₂) decomposition to generate hydroxyl radical (OH) and degradation of various pollutants under solar irradiation. The contribution of the increase in MoS₂ edges for decomposing H₂O₂ was 0.0698 min^-1. That is 9.83 times the rate of the original MoS₂ edges resulting from the vertical structure. Specially, the catalyst degraded various aromatic pollutants even in the dark by releasing electrons stored in its graphite component to realize "memory catalysis". Also, it exhibited high degradation efficiency under outdoor solar irradiation. The catalyst was easily separated from the treated water, avoiding complex separation processes. All these features suggest this catalyst has great potential in practical water and sewage treatment applications.