Synthesis and electrochemical performances of cobalt sulfides/graphene nanocomposite as anode material of Li-ion battery

The powders of cobalt sulfide were successfully synthesized using hydrothermal technique at various temperatures (180, 200 and 220 °C). X-ray diffraction revealed that the resulting samples are the hexagonal CoS, and the cubic Co₉S₈. Fourier transform infrared further verified the cobalt sulfide formation, showing Co-S band vibrations at 600 cm^-1 across all samples. Scanning electron microscopy unveiled diverse hierarchical morphologies with notable porosity. Energy-dispersive X-ray microanalysis revealed the purity of samples, showing no traces of impurities. Electrochemical impedance spectroscopy showed a charge transfer phenomenon in the high-frequency range. The optical band gap energies (Eg) were determined using the Tauc model, yielding 1.95 eV for CoS and 2.81 eV for Co₉S₈. The photocatalytic efficiency of cobalt sulfides for dye degradation was assessed employing methylene blue as a model colorant through photocatalytic technology. This study underscores all samples as efficient and stable photocatalysts, especially the CoS-Co₉S₈ mixture phases.

High-energy density lithium-sulfur battery is considered as one of the most potential new-generation energy-storage technologies. Nevertheless, the capacity decays rapidly due to severe volumetric change of sulfur, dissolution and slow redox kinetics of intermediate polysulfides, and instability of lithium anode. Herein, a novel highly conductive porous sulfur cathode host composed of graphene aerogel and polar Co₉S₈ nanoparticle is designed to address these obstacles. The porous conductive framework not only provides channels for rapid conduction of electron and lithium ion, but also provides adequate space to physically confine the lithium polysulfides and accommodate the volume expansion. Both experimental and theoretical calculations demonstrate that the in-situ uniformly deposited Co₉S₈ nanoparticles can effectively bind polar lithium polysulfides and catalyze their interconversion, and the shuttle effect is therefore effectively suppressed. The Co₉S₈-GA/S cathode exhibits high specific discharge capacity (1219.1 mAh g⁻¹) and high areal specific capacity (14.3 mAh m⁻²) at 0.1 C, low shuttle constant (0.15 h⁻¹), excellent rate performance (625.6 mAh g⁻¹/7.4 mAh m⁻² at 5 C), outstanding long cyclic stability (low decay of 0.024 %/cycle during 1000 cycles at 2 C). This study demonstrates a promising aerogel strategy to design high-performance composite cathode for lithium-sulfur battery.

Two-dimensional materials, including graphene and its derivatives, MXenes, and transition metal dichalcogenides, have attracted significant research attention due to their unique physicochemical properties. Among the various applications of these materials, energy storage and conversion have gained particular importance in light of the ongoing energy crisis. In this review, a critical evaluation is presented, focusing on the fundamentals, recent developments, and future perspectives of two-dimensional materials as anodes in lithium-ion batteries. The emphasis of this evaluation lies specifically on the years between 2010 and 2023. The review will primarily delve into the design and manipulation of advanced interface architectures for anodes, the latest developments, and the composition structure-property relationship of transition metal dichalcogenides (TMDs), MXenes, molybdenum disulfide (MoS₂), tungsten sulfide (WS₂), and black phosphorous (BP). The main focus of the presented review revolves around modification techniques that hold great potential in energy storage applications and other energy-related fields. The exceptional characteristics of these materials, including efficient ion transport across layers and large surface areas facilitating enhanced ion adsorption and accelerated surface redox reactions, contribute to their promising performance. While we have accumulated about twenty years of experience in energy conversion applications, particularly in lithium-ion batteries, we found that a large number of articles have been published on electrodes and electrolytes. However, a critical discussion about the composition structure-property relationship, along with challenges and optimizing strategies for anodes, is still lacking. Therefore, this review aims to fill that gap. Additionally, an overview of recent research advances is provided, focusing on the application of 2D materials in advanced energy storage systems beyond conventional lithium-ion batteries. Key findings and strategies employed to address associated challenges are examined while considering the prospects of these materials in the field.

In the present work, microspheres of CoS are synthesized by most adoptable hydrothermal method. The synthesized material is figured out by numerous characteristic techniques. Further, the prepared CoS material is used as electrode material for supercapacitor and high specific capacity of 112.62 mAh g⁻¹ is obtained at 1 A g⁻¹. Furthermore, the capacity of sole product is boosted by adding a small amount of multi-walled carbon nanotubes (MWCNTs) and improved specific capacity of 158 mAh g⁻¹ is obtained from MWCNT/CoS at 1 A g⁻¹. Owing to high specific capacity of composite, aqueous asymmetric supercapacitor (ASC) is designed by MWCNT/CoS as a positive electrode and activated carbon (AC) as a negative electrode. The high energy density of 31.6 W h kg⁻¹ is obtained at the power density of 750 Wh kg⁻¹ from MWCNT/CoS//AC. In addition, two parallel connected red color LEDs, kitchen timer and a motor fan are functionalized by two MWCNT/CoS//AC devices.

Herein, composites consisting of Co₉S₈ nanoparticles coated by N-doped carbon coating layer and self-grown N-doped carbon nanotubes (Co₉S₈@NC-NCNTs) were prepared and used for lithium storage. Co₉S₈@NC-NCNTs composites can deliver reversible capacities of 627 mAh·g⁻¹ at 0.2 A·g⁻¹ and 531 mAh·g⁻¹ at 0.5 A·g⁻¹, and are able to maintain a specific capacity of 494 mAh·g⁻¹ at 2.0 A·g⁻¹ after 1000 cycles. The excellent properties should be attributed to NC-NCNTs coating layer in composites which can not only promote the rapid transport of electrons and ions, but also ensure integrity of electrodes during charge–discharge processes.

Transition metal sulfides(TMSs) are an ideal alternative for use in lithium-ion batteries(LIBs) owing to their high theoretical capacity and environmental advantages. However, bulk expansion problems of TMSs and the classical method of electrode synthesis limit their large-scale development. In this study, 3D hydrangea-shaped Co₉S₈ @graphene nanocomposites were successfully prepared by one-step in-situ pyrolytic sulfidation. The resulting Co₉S₈ @graphene composites were tested as anodes of LIBs and showed excellent electrochemical properties with a high discharge specific capacity of 1530.3mAh·g⁻¹ at a current density of 0.1 A·g⁻¹, superior multiplicative properties reaching 415.7mAh·g⁻¹ at a current density of 5 A·g⁻¹, and rapid recovery to 726.4mAh·g⁻¹ when the current density returned to its initial value. The electrodes also displayed superior capacity retention and cycling stability at high current densities with a stable discharge capacity of 550mAh·g⁻¹ after 1000 cycles at a current density of 1 A·g⁻¹. These features were attributed to the 3D hydrangea-like graphene structure, which greatly increased the specific surface area of the material, facilitating contact with the electrolyte during electrochemical reactions. The nanoparticles also provided more space, thereby improving the volume expansion of the material during the electrochemical processes. In sum, these findings offer a new synthetic route to future preparation of metal sulphide@graphene composites.