Wafer-like FeSe2-NiSe2/C nanosheets as efficient anode for high-performances lithium batteries

Theoretical Investigation of Stacked Two-Dimensional Transition-Metal Dichalcogenide Materials: The Role of Chemical Species and Number of Monolayers

We report a theoretical investigation, based on density functional theory calculations, of the role of chalcogen species and the number of monolayers in the physical-chemical properties of multilayer two-dimensional transition-metal dichalcogenides (TMDs, MQ2), where M belongs to groups 8 and 10 of the periodic table, Q = S, Se, or Te, and the multilayer is composed of 1 to 6 layers. From the analysis of structural energetic, and electronic properties, we found significant changes in lattice parameters and exfoliation energies as a function of the number of layers, particularly affected by the chalcogen Q species. The TMDs in group 8 exhibit similar lattice parameters for the same choice of chalcogens, making them suitable for constructing commensurate heterostructures, while the crystal phase and the lattice parameter of the TMDs in group 10 strongly depend on the choice of the transition-metal species. Furthermore, the decreasing trend of electronegativity from S to Te results in stronger exfoliation energies due to lower surface charges, thus governing the structural and electronic characteristics of few-layer TMDs. We find unexpected electronic characteristics, such as band gap increases driven by spin-orbit coupling for certain compositions, the emergence of polarization electric fields due to point inversion symmetry breaking, and semiconductor-to-metal transitions with minimal layer additions to the monolayer. The presence of sulfur improves the sensitivity of the surface properties, enabling precise tuning of band edge positions with the layer number.

Heterogeneous Engineering Strategy Derived In Situ Carbon-Encased Nickel Selenides Enabling Superior LIBs/SIBs with High Thermal Safety

Nowadays, the extended usage of lithium/sodium ion batteries (LIBs/SIBs) encounters nerve-wracking issues, including a lack of suitable reservoirs and high thermal runaway hazards. Although using TiO2 and Li4Ti5O12 has been confirmed to be effective in improving battery safety, their low theoretical capacities inevitably cause damage to the electrochemical performance of the battery. Achieving win-win results has become an urgent necessity. This study designed a metal-organic framework (MOF)-derived in situ carbon-coated metal selenide (Ni-Se@G@C) as the anode. When the current density is 0.1-0.3 A g-1, the initial capacity of LIBs reaches 993.2 mAh g-1, which increases to 1478.9 mAh g-1 after running 800 cycles. When running at 2 A g-1, the cell also offers a relatively high capacity of 458.3 mAh g-1 after 1500 cycles. After the replacement of graphite with Ni-Se@G@C, the self-heating temperature (T0) and thermal runaway triggering temperature (T1) of half and full cells are significantly increased. Meanwhile, the maximum thermal runaway temperature (T2) and maximal heating release rate (HRRmax) are significantly reduced. Of note, the usage of Ni-Se@G@C enables the battery with superior cycling and rate performance. When used in SIBs, the cell gives an initial discharge capacity of 624.9 mAh g-1, which still remains at 269.4 mAh g-1 after running 200 cycles at 1 A g-1. Notably, Ea of the Ni-Se@G@C cell is 5.6 times higher than that of the graphite cell, corroborating the promoted safety performance. This work provides a new paradigm for MOF-derived micro/nanostructures, enabling the battery with an excellent electrochemical and safety performance portfolio.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

CoSe nanoparticles in-situ grown in 3D honeycomb carbon for high-performance lithium storage

Although transition metal selenides are considered to be extremely promising anode materials for lithium-ion batteries (LIBs), severe volume changes and low electronic conductivity are their huge and unavoidable challenges. To solve these problems, CoSe nanoparticles in-situ grown on the inner surface of every macropore of 3D honeycomb C is successfully synthesized by three simple steps: dense assembling of polystyrene spheres, calcination and gaseous selenylation. The sizes of CoSe and honeycomb pores are 10-15 nm and 190 nm, respectively. The content of CoSe is 72 wt%. This unique architecture guarantees high electrochemical activity, rapid reaction kinetics and excellent structural stability of CoSe, as identified by cycling and rate performance measurements, various electrochemical kinetics analyses and ex-situ characterization of the cycled electrode material. As a result, the CoSe@honeycomb C anode exhibits extraordinary cycling performance (823.5 mAh g^-1 after 200 cycles at 0.5 A g^-1, 610.1 mAh g^-1 after 250 cycles at 2 A g^-1, 247 mAh g^-1 after 1500 cycles at 5 A g^-1) and exceptional rate capability (261.9 mAh g^-1 at 10 A g^-1, 1491.4 mAh g^-1 at 0.1 A g^-1), demonstrating that it is a potential anode material for high-performance LIBs.

Hierarchical MXene/transition metal chalcogenide heterostructures for electrochemical energy storage and conversion

MXenes have gained rapidly increasing attention owing to their two-dimensional (2D) layered structures and unique mechanical and physicochemical properties. However, MXenes have some intrinsic limitations (e.g., the restacking tendency of the 2D structure) that hinder their practical applications. Transition metal chalcogenide (TMC) materials such as SnS, NiS, MoS₂, FeS₂, and NiSe₂ have attracted much interest for energy storage and conversion by virture of their earth-abundance, low costs, moderate overpotentials, and unique layered structures. Nonetheless, the intrinsic poor electronic conductivity and huge volume change of TMC materials during the alkali metal-ion intercalation/deintercalation process cause fast capacity fading and poor-rate and poor-cycling performances. Constructing heterostructures based on metallic conductive MXenes and highly electrochemically active TMCs is a promising and effective strategy to solve these problems and enhance the electrochemical performances. This review highlights and discusses the recent research development of MXenes and hierarchical MXene/TMC heterostructures, with a focus on the synthesis strategies, surface/heterointerface engineering, and potential applications for lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, electrocatalysis, and photocatalysis. The critical challenges and perspectives of the future development of MXenes and hierarchical MXene/TMC heterostructures for electrochemical energy storage and conversion are forecasted.

Bismuth selenide nanosheets confined in thin carbon layers as anode materials for advanced potassium-ion batteries

A composite of Bi2Se3 nanosheets confined in ultrathin carbon layers is synthesized. The carbon layers buffer the volume variation and enhance the electronic conductivity of the electrode, resulting in improved potassium-ion storage performance.

Electronic modulation of nickel selenide by copper doping and in situ carbon coating towards high-rate and high-energy density lithium ion half/full batteries

Over the past decades, metal selenides have drawn considerable attention due to their high theoretical specific capacity. However, huge volume changes and sluggish electrochemical transfer kinetics hinder their applications in energy storage and conversion. In this work, we demonstrate an efficient and ingenious synthesis strategy to regulate nickel selenide electrodes by the introduction of copper and in situ coating with carbon (Cu-NiSe2@C). When used as anodes for lithium-ion batteries, the as-synthesized Cu-NiSe2@C delivered a high capacity of 1630 mA h g-1 at 1.0 A g-1 after 200 cycles and excellent rate performance as well as long-term cycling stability with a high capacity of 489 mA h g-1 at 10 A g-1 after 20 000 cycles. When coupled with a commercial LiFePO4 cathode, the full cells showed a high capacity of 463 mA h g-1 at 0.2 A g-1. Their superior electrochemical performance can be attributed to the synergistic effect of the in situ carbon coating and copper doping, which can promote the electron/ion transfer kinetics, as well as alleviate the volume expansion during cycling. This work will open new opportunities for the development of high-performance anodes for lithium storage.