Large Interlayer Spacing of Few-Layered Cobalt-Tin-Based Sulfide Providing Superior Sodium Storage

Ultrafast Synthesis of Oxygen Vacancy-Rich MgFeSiO4 Cathode to Boost Diffusion Kinetics for Rechargeable Magnesium-Ion Batteries

Rechargeable magnesium ion batteries (RMBs) have drawn extensive attention due to their high theoretical volumetric capacity and low safety hazards. However, divalent Mg ions suffer sluggish mobility in cathodes owing to the high charge density and slow insertion/extraction kinetics. Herein, it is shown that an ultrafast nonequilibrium high-temperature shock (HTS) method with a high heating/quenching rate can instantly introduce oxygen vacancies into the olivine-structured MgFeSiO4 cathode (MgFeSiO4-HTS) in seconds. As a proof of concept, the MgFeSiO4-HTS exhibits a higher electrochemical property and fast insertion/extraction kinetics in comparison to those prepared from the conventional sintering method. The MgFeSiO4-HTS displays remarkable long-term cycling lifespan properties with a reversible capacity of 85.65 and 54.43 mAh g-1 over 500 and 1600 cycles at 2 and 5 C, respectively. Additionally, by combining the electrochemical experiments and density functional theory calculations, oxygen vacancies can weaken the interaction and energy barrier between the Mg2+ ions and the cathode, enhancing the Mg2+ diffusion kinetics.

Modulating the electronic structure of CoS2 by Sn doping boosting urea oxidation for efficient alkaline hydrogen production

Urea electrocatalytic oxidation afforded by renewable energies is highly promising to replace the sluggish oxygen evolution reaction in water splitting for hydrogen production while realizing the treatment of urea-rich waste water. Therefore, the development of efficient and cost-effective catalysts for water splitting assisted by urea is highly desirable. Herein, Sn-doped CoS₂ electrocatalysts were reported with the engineered electronic structure and the formation of Co-Sn dual active sites for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), respectively. Consequently, the number of active sites and the intrinsic activity were enhanced simultaneously and the resultant electrodes exhibited outstanding electrocatalytic activity with a very low potential of 1.301 V at 10 mA·cm^-2 for UOR and an overpotential of 132 mV at 10 mA·cm^-2 for HER. Therefore, a two-electrode device was assembled by employing Sn(2)-CoS₂/CC and Sn(5)-CoS₂/CC and the constructed cell required only 1.45 V to approach a current density of 10 mA·cm^-2 along with good durability for at least 95 h assisted by urea. More importantly, the assembled electrolyzer can be powered by commercial dry battery to generate numerous gas bubbles on the surface of the electrodes, demonstrating the high potential of the as-fabricated electrodes for applications in hydrogen production and pollutant treatment at a low-voltage electrical energy input.

Dual Carbon Design Strategy for Anodes of Sodium-Ion Battery: Mesoporous CoS2/CoO on Open Framework Carbon-Spheres with rGO Encapsulating

Transition metal sulfides and oxides with high theoretical capacities have been regarded as promising anode candidates for a sodium-ion battery (SIB); however, they have critical issues including sluggish electrochemical kinetics and poor long-term stability. Herein, a dual carbon design strategy is proposed to integrate with highly active heterojunctions to overcome the above issues. In this new design, CoS₂/CoO hollow dodecahedron heterojunctions are sandwiched between open framework carbon-spheres (OFCs) and a reduced graphene oxide (rGO) nanomembrane (OFC@CoS₂/CoO@rGO). The CoS₂/CoO heterojunctions effectively promote electron transfer on their surface and provide more electrochemical active sites through their hierarchical hollow structures assembled by nanodots. Meanwhile, the dual-carbon framework forms a highly conductive network that enables a better rate capability. More importantly, the dual carbon can greatly buffer volume expansion and stable reaction interfaces of electrode material during the charge/discharge process. Benefitting from their synergistical effects, the OFC@CoS₂/CoO@rGO electrode achieves a high reversible capacity of 460 mAh g^-1 at 0.05 A g^-1 and still maintains 205.3 mAh g^-1 even when current density is increased by 200 times when used as an anode material for SIBs. Their cycling property is also remarkable with a maintained capacity of 161 mAh g^-1 after 3500 charging/discharging cycles at a high current density of 1 A g^-1. The dual-carbon strategy is demonstrated to be effective for enhanced reaction kinetics and long-term cycling property, providing siginificant guidance for preparing other high-performance electrode materials.

Solid Solution Metal Chalcogenides for Sodium-Ion Batteries: The Recent Advances as Anodes

The sodium-ion battery (SIB) has attracted ever growing attention as a promising alternative of the lithium-ion battery (LIB). Constructing appropriate anode materials is critical for speeding up the application of SIB. This review aims at guiding anode design from the material's perspective, and specifically focusing on solid solution metal chalcogenide anode. The sodium ion storage mechanisms of a solid solution metal chalcogenide anode is overviewed on basis of the elements it is composed of, and discusses how the solid solution character alters the electrochemical performances through diffusion and surface-controlled processes. In addition, by classifying solid solution metal chalcogenide as cation and anion, their recent applications are updated, and understanding the roles of guest elements in improving the electrochemical behaviors of a solid solution metal chalcogenide is carried out. After that, discussion of possible strategies to further optimize these anode materials in the future, flowing from crystal structure design to morphology control and finally to the intimacy improvement between conductive matrix and solid solution metal chalcogenide are also provided.

Ammonium Intercalation Induced Expanded 1T-Rich Molybdenum Diselenides for Improved Lithium Ion Storage

Transition metal dichalcogenides (TMDs), particularly molybdenum diselenides (MoSe₂), have the merits of their unique two-dimensional (2D) layered structures, large interlayer spacing (∼0.64 nm), good electrical conductivities, and high theoretical capacities when applied in lithium-ion batteries (LIBs) as anode materials. However, MoSe₂ remains suffering from inferior stability as well as unsatisfactory rate capability because of the unavoidable volume expansion and sluggish charge transport during lithiation-delithiation cycles. Herein, we develop a simultaneous reduction-intercalation strategy to synthesize expanded MoSe₂ (e-MoSe₂) with an interlayer spacing of 0.98 nm and a rich 1T phase (53.7%) by rationally selecting the safe precursors of ethylenediamine (NH₂C₂H₄NH₂), selenium dioxide (SeO₂), and sodium molybdate (Na₂MoO₄). It is noteworthy that NH₂C₂H₄NH₂ can effectively reduce SeO₂ and MoO₄^2- forming MoSe₂ nanosheets; in the meantime, the generated ammonium (NH₄⁺) efficiently intercalates between MoSe₂ layers, leading to charge transfer, thus stabilizing 1T phases. The obtained e-MoSe₂ exhibits high capacities of 778.99 and 611.40 mAh g^-1 at 0.2 and 1 C, respectively, together with excellent cycling stability (retaining >90% initial capacity at 0.2 C over 100 charge-discharge cycles). It is believed that the material design strategy proposed in this paper provides a favorable reference for the synthesis of other transition metal selenides with improved electrochemical performance for battery applications.