Three-Dimensional Porous Nitrogen-Doped Carbon Nanosheet with Embedded NixCo3-xS4 Nanocrystals for Advanced Lithium-Sulfur Batteries

LDH-derived Co0.5Ni0.5Te2 dispersed in 3D carbon sheets as a separator modifier to enable kinetics-accelerated lithium-sulfur batteries

Lithium-sulfur batteries are considered powerful candidates for the next generation of advanced energy-storage systems owing to their high energy density and theoretical specific capacity. However, their practical commercial feasibility has been hampered by their sluggish kinetics and severe shuttle effect. Hence, a novel hybrid comprising NiCo-LDH-derived Co0.5Ni0.5Te2 nanoparticles grafted on 3D carbon sheets was rationally constructed through facile steps and served as a functional separator modifier for a lithium-sulfur battery. It was found that the 3D cross-linked conductive network structure of the hybrid is conductive to continuous electron transfer. In addition, well-dispersed Co0.5Ni0.5Te2 nanoparticles with hexahedral morphology offer an ample sulfophilic surface to chemically anchor and catalyze the redox dynamics of sulfur species. It was proven that the dynamic conversion of sulfur-involved reactions was effectively promoted and the utilization of polysulfides was boosted. The related cells demonstrated attractive long-cycling durability (784.8 mA h g-1 at 2 C after 500 cycles) and an excellent rate performance (699.5 mA h g-1 even at 7 C). Furthermore, when sulfur loading reached 6.89 mg cm-2, areal capacity could still be maintained at 6.40 mA h cm-2 after 50 cycles at 0.2 C. This work provides a promising strategy to design a multifunctional separator modifier and promotes the exploration of metal tellurides to engineer advanced kinetics-accelerated lithium-sulfur batteries.

Electrocatalytic Synthesis of Urea: An In-depth Investigation from Material Modification to Mechanism Analysis

Industrial urea synthesis production uses NH3 from the Haber-Bosch method, followed by the reaction of NH3 with CO2, which is an energy-consuming technique. More thorough evaluations of the electrocatalytic C-N coupling reaction are needed for the urea synthesis development process, catalyst design, and the underlying reaction mechanisms. However, challenges of adsorption and activation of reactant and suppression of side reactions still hinder its development, making the systematic review necessary. This review meticulously outlines the progress in electrochemical urea synthesis by utilizing different nitrogen (NO3 -, N2, NO2 -, and N2O) and carbon (CO2 and CO) sources. Additionally, it delves into advanced methods in materials design, such as doping, facet engineering, alloying, and vacancy introduction. Furthermore, the existing classes of urea synthesis catalysts are clearly defined, which include 2D nanomaterials, materials with Mott-Schottky structure, materials with artificially frustrated Lewis pairs, single-atom catalysts (SACs), and heteronuclear dual-atom catalysts (HDACs). A comprehensive analysis of the benefits, drawbacks, and latest developments in modern urea detection techniques is discussed. It is aspired that this review will serve as a valuable reference for subsequent designs of highly efficient electrocatalysts and the development of strategies to enhance the performance of electrochemical urea synthesis.

A Porous Hexagonal Prism Shaped C-In2-xCoxO3 Electrocatalyst to Expedite Bidirectional Polysulfide Redox in Li-S Batteries

The shuttling behavior of soluble lithium polysulfides (LPSs) extremely restricts the practical application of lithium sulfur batteries (Li-S batteries). Herein, the hollow porous hexagonal prism shaped C-In_2-xCo_xO₃ composite is synthesized to restrain the shuttle effect and accelerate reaction kinetics of LPSs. The novel hexagonal prism porous carbon skeleton not only provides a stable physical framework for sulfur active materials but also facilitates efficient electron transferring and lithium ion diffusion. Meanwhile, the polar In_2-xCo_xO₃ is equipped with strong adsorption capacity for LPSs, which is confirmed by density functional theory (DFT) calculations, helping to anchor LPSs. More importantly, the doping of Co regulates the electronic structure environment of In₂O₃, expedites the electron transmission, and bidirectionally improves the catalytic conversion ability of LPSs and nucleation-decomposition of Li₂S. Benefiting from the above advantages, the electrochemical performance of Li-S batteries has been greatly enhanced. Therefore, the C-In_2-xCo_xO₃ cathode presents a good rate performance, which exhibits a low-capacity fading rate of 0.052% per cycle over 800 cycles at 5 C. Especially, even under a high sulfur loading of 4.8 mg cm^-2, the initial specific capacity is as high as 903 mAh g^-1, together with a superior capacity retention of 85.6% after 600 cycles at 0.5 C.

Facile Synthesis of NixCo3-xS4 Microspheres for High-Performance Supercapacitors and Alkaline Aqueous Rechargeable NiCo-Zn Batteries

Electrochemical energy storage devices (EESDs) have caused widespread concern, ascribed to the increasing depletion of traditional fossil energy and environmental pollution. In recent years, nickel cobalt bimetallic sulfides have been regarded as the most attractive electrode materials for super-performance EESDs due to their relatively low cost and multiple electrochemical reaction sites. In this work, NiCo-bimetallic sulfide Ni_xCo_3-xS₄ particles were synthesized in a mixed solvent system with different proportion of Ni and Co salts added. In order to improve the electrochemical performance of optimized Ni_2.5Co_0.5S₄ electrode, the Ni_2.5Co_0.5S₄ particles were annealed at 350 °C for 60 min (denoted as Ni_2.5Co_0.5S₄-350), and the capacity and rate performance of Ni_2.5Co_0.5S₄-350 was greatly improved. An aqueous NiCo-Zn battery was assembled by utilizing Ni_2.5Co_0.5S₄-350 pressed onto Ni form as cathode and commercial Zn sheet as anode. The NiCo-Zn battery based on Ni_2.5Co_0.5S₄-350 cathode electrode delivers a high specific capacity of 232 mAh g^-1 at 1 A g^-1 and satisfactory cycling performance (65% capacity retention after 1000 repeated cycles at 8 A g^-1). The as-assembled NiCo-Zn battery deliver a high specific energy of 394.6 Wh kg^-1 and long-term cycling ability. The results suggest that Ni_2.5Co_0.5S₄-350 electrode has possible applications in the field of alkaline aqueous rechargeable electrochemical energy storage devices for supercapacitor and NiCo-Zn battery.

Active Sulfur-Host Material VS4 with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li-S Batteries

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS₄/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS₄/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li₂S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS₄/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS₄. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS₄/rGO cathode displays a high specific capacity of 1332.6 mA h g^-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g^-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm^-2, it still can deliver 756.2 mA h g^-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S₈ → Li₂S → β-S₈ (first cycle) and then β-S₈ ↔ Li₂S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.

Crystalline Multi-Metallic Compounds as Host Materials in Cathode for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is one of the most promising next-generation rechargeable batteries. Lots of fundamental research has been done for the problems during cycling like capacity fading and columbic efficiency reducing owing to severe diffusion and migration of polysulfide intermediates. In the early stage, a wide variety of carbon materials are used as host materials for sulfur to enhance electrical conductivity and adsorb soluble polysulfides. Beyond carbon materials, metal based polar compounds are introduced as host materials for sulfur because of their strong catalytic activity and adsorption ability to suppress the shuttle effect. In addition, relatively high density of metal compounds is helpful for increasing volumetric energy density of Li-S batteries. This review focuses on crystalline multi-metal compounds as host materials in sulfur cathodes. The multi-metal compounds involve not only transition metal composite oxides with specific crystalline structures, binary metal chalcogenides, double or complex salts, but also the metal compounds doped or partially substituted by other metal ions. Generally, for the multi-metal compounds, microstructure and morphologies in micro-nano scale are very significant for mass transfer in electrodes; moreover, adsorption and catalytic ability for polysulfides make fast kinetics in the electrode processes.

MXene-Derived Tin O2 n- 1 Quantum Dots Distributed on Porous Carbon Nanosheets for Stable and Long-Life Li-S Batteries: Enhanced Polysulfide Mediation via Defect Engineering

The application of Li-S batteries has been hindered by the shuttling behavior and sluggish reaction kinetics of polysulfides. Here an effective polysulfide immobilizer and catalytic promoter is developed by proposing oxygen-vacancy-rich Tin O2 n -1 quantum dots (OV-Tn QDs) decorated on porous carbon nanosheets (PCN), which are modulated using Ti3 C2 Tx MXene as starting materials. The Tn QDs not only confine polysulfides through strong chemisorption but also promote polysulfide conversion via redox-active catalysis. The introduction of oxygen vacancies further boosts the immobilization and conversion of polysulfides by lowering the adsorption energy and shortening the bond lengths. The PCN provides a physical polysulfide confinement as well as a flexible substrate preventing OV-Tn QDs from aggregation. Moreover, the two building blocks are conductive, thereby effectively improving the electron/charge transfer. Finally, the ultrasmall size of QDs along with the porous structure endows OV-Tn QDs@PCN with large specific surface area and pore volume, affording adequate space for S loading and volume expansion. Therefore, the OV-Tn QDs@PCN/S delivers a high S loading (79.1 wt%), good rate capability (672 mA h g-1 at 2 C), and excellent long-term cyclability (88% capacity retention over 1000 cycles at 2 C). It also exhibits good Li+ storage under high S-mass loading and lean electrolyte.

Theoretical investigation on lithium polysulfide adsorption and conversion for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries have shown great application prospects as next-generation energy storage systems due to their high theoretical capacity and high energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as their sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs). To date, significant research has been focused on the confinement adsorption and catalytic conversion of LiPSs using theoretical or/and experimental methods. Among them, theoretical calculations are highly attractive to observe complex LiPS conversion reactions, which facilitate the rational design of S mediators for high-performance Li-S batteries. In this review, we summarize and discuss the recent advances in the adsorption and conversion of LiPSs from the viewpoint of theoretical calculations. Moreover, a set of theoretical principles to guide the screening of suitable host materials for Li-S batteries is presented and discussed. Finally, some personal insights about the future challenges and the focus of research in this field are presented, which will push a milestone step toward high-efficiency and long-life Li-S batteries.