The Quest for Polysulfides in Lithium–Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study

Confocal Raman spectra of a lithium–sulfur battery electrolyte are recorded operando in a depth‐of‐discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.     

Synthesis of 2D/2D Structured Mesoporous Co3O4 Nanosheet/N‐Doped Reduced Graphene Oxide Composites as a Highly Stable Negative Electrode for Lithium Battery Applications

Mesoporous Co₃O₄ nanosheets (Co₃O₄‐NS) and nitrogen‐doped reduced graphene oxide (N‐rGO) are synthesized by a facile hydrothermal approach, and the N‐rGO/Co₃O₄‐NS composite is formulated through an infiltration procedure. Eventually, the obtained composites are subjected to various characterization techniques, such as XRD, Raman spectroscopy, surface area analysis, X‐ray photoelectron spectroscopy (XPS), and TEM. The lithium‐storage properties of N‐rGO/Co₃O₄‐NS composites are evaluated in a half‐cell assembly to ascertain their suitability as a negative electrode for lithium‐ion battery applications. The 2D/2D nanostructured mesoporous N‐rGO/Co₃O₄‐NS composite delivered a reversible capacity of about 1305 and 1501 mAh g^?1 at a current density of 80 mA g^?1 for the 1st and 50th cycles, respectively. Furthermore, excellent cyclability, rate capability, and capacity retention characteristics are noted for the N‐rGO/Co₃O₄‐NS composite. This improved performance is mainly related to the existence of mesoporosity and a sheet‐like 2D hierarchical morphology, which translates into extra space for lithium storage and a reduced electron pathway. Also, the presence of N‐rGO and carbon shells in Co₃O₄‐NS should not be excluded from such exceptional performance, which serves as a reliable conductive channel for electrons and act as synergistically to accommodate volume expansion upon redox reactions. Ex‐situ TEM, impedance spectroscopy, and XPS, are also conducted to corroborate the significance of the 2D morphology towards sustained lithium storage.     

Nitrogen‐Doped Mesoporous Carbon‐Encapsulated MoO2 Nanobelts as a High‐Capacity and Stable Host for Lithium‐Ion Storage

N‐doped mesoporous carbon‐capped MoO₂ nanobelts (designated as MoO₂@NC) were synthesized and applied to lithium‐ion storage. Owing to the stable core–shell structural framework and conductive mesoporous carbon matrix, the as‐prepared MoO₂@NC shows a high specific capacity of around 700 mA h g⁻¹ at a current of 0.5 A g⁻¹, excellent cycling stability up to 100 cycles, and superior rate performance. The N‐doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core–shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO₂@NC to be a suitable and promising material for lithium ion battery.     

A Sustainable Redox-Flow Battery with an Aluminum-Based,Deep-Eutectic-Solvent Anolyte

Nonaqueous redox-flow batteries are an emerging energy storage technology for grid storage systems, but the development of anolytes has lagged far behind that of catholytes due to the major limitations of the redox species, which exhibit relatively low solubility and inadequate redox potentials. Herein, an aluminum-based deep-eutectic-solvent is investigated as an anolyte for redox-flow batteries. The aluminum-based deep-eutectic solvent demonstrated a significantly enhanced concentration of circa 3.2 m in the anolyte and a relatively low redox potential of 2.2 V vs. Li⁺/Li. The electrochemical measurements highlight that a reversible volumetric capacity of 145 Ah L⁻¹ and an energy density of 189 Wh L⁻¹ or 165 Wh kg⁻¹ have been achieved when coupled with a I₃⁻/I⁻ catholyte. The prototype cell has also been extended to the use of a Br₂-based catholyte, exhibiting a higher cell voltage with a theoretical energy density of over 200 Wh L⁻¹. The synergy of highly abundant, dendrite-free, multi-electron-reaction aluminum anodes and environmentally benign deep-eutectic-solvent anolytes reveals great potential towards cost-effective, sustainable redox-flow batteries.     

Singlet Oxygen during Cycling of the Aprotic Sodium–O2 Battery

Aprotic sodium–O₂ batteries require the reversible formation/dissolution of sodium superoxide (NaO₂) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO₂, a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Herein we show that singlet oxygen (¹O₂) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in‐ and ex‐situ via a ¹O₂ trap that selectively and rapidly forms a stable adduct with ¹O₂. The ¹O₂ formation mechanism involves proton‐mediated superoxide disproportionation on discharge, rest, and charge below ca. 3.3 V, and direct electrochemical ¹O₂ evolution above ca. 3.3 V. Trace water, which is needed for high capacities also drives parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.     

Novel ferrocene-containing amphiphilic block copolymer nanoparticles as high-capacity charge carriers in aqueous redox flow systems

Size-exclusion polymer electrolytes are promising charge carriers to diminish the crossover and allowing commercially available low-cost porous membranes in redox flow batteries. Boosting the solubility in water and maximizing the number of redox sites to enhance the capacity of these polymeric systems is challenging. New highly water dispersed amphiphilic diblock copolymers are reported here, with an average concentration value of 1.7 10^?3 mmol of Ferrocene (Fc)-linked moieties per mg of polymer, determined by total X-ray reflection fluorescence. These redox amphiphilic block copolymers are stabilized in water as spherical nanoparticles (20 nm) by using a simple phase solvent inversion procedure. We evidence a maximum polymer dispersibility value of 6 g/L in water, for long-term stable polymer nanoparticle suspensions, yielding a theoretical capacity value of 4.78 mAh at 10.5 mM Fc. Further adjustment of the ionic conductivity and pH of these stable redox block copolymer suspensions has rendered a conductivity value of 44.5 mS/cm at pH values close to a neutral one, by adding a variety of salt supports. Studies using a 3-electrode configuration cell reveal an efficient charge transport between each of the Fc motifs in the polymer nanoparticle. A capacity value of 3.1 mAh with no transient of the polymer nanoparticles crosswise the cheap porous membrane is evidenced when cycled as polycatholyte material in a Zn hybrid aqueous redox flow battery. The particle size and electronic changes of these novel amphiphilic redox block copolymer electrolytes during consecutive redox cycles have also been monitored by dynamic light scattering and ultraviolet-visible spectroscopy, respectively. The analysis of the results enables the understanding of the main mechanisms behind their non-fully reversible capacity. Among them, aggregation and sedimentation, along with retention inside the graphite felt electrode acting the latter as a filter. These insights will aid the design of future polymer electrolyte materials and redox flow battery components with better performance and cost.     

Two-dimensional MgSiP_2 with anisotropic electronic properties and good performances for Na-ion batteries

Using the global particle-swarm optimization method and density functional theory,we predict a new stable two-dimensional layered material:MgSiP_2 with a low-buckled honeycomb lattice.Our HSE06 calculation shows that MgSiP_2 is an indirect-gap semiconductor with a band-gap of 1.20 eV,closed to that of bulk silicon.More remarkably,MgSiP2 exhibits worthwhile anisotropy along with electron and hole carrier mobility.A ultrahigh electron mobility is even up to 1.29 × 104 cm~2 V ~1 s ~1.while the hole mobility is nearly zero along the a direction.The large difference of the mobility between electron and hole together with the suitable band-gap suggest that MgSiP_2 may be a good candidate for solar cell or photochemical catalysis material.Furthermore,we explore MgSiP2 as an anode for sodium-ion batte ries.Upon Na adsorption,the semiconducting MgSiP2 transforms to a metallic state,ensuring good electrical conductivity.A maximum theoretical capacity of 1406 mAh/g,a small volume change(within 9.5%),a small diffusion barrier(～0.16 eV) and low average open-circuit voltages(～0.15 V) were found fo r MgSiP2 as an anode for sodium-ion batteries.These results are helpful to deepen the understanding of MgSiP2 as a nanoelectronic device and a potential anode for Na-ion batteries.     

Copper-cobalt-nickel oxide nanowire arrays on copper foams as self-standing anode materials for lithium ion batteries

Numerous scientists are in the pursuit of energy storage materials with high energy and high power density by assembly of electrochemically active materials into conductive scaffolds, owing to the emerging need for next-generation energy storage devices. In this architectures, the active materials bonded to the conductive scaffold can provide a robust and free-standing structure, which is crucial to the fabrication of materials with high gravimetric capacity. Thus, hierarchical copper-cobalt-nickel ternary oxide (CuCoNi-oxide) nanowire arrays grown from copper foam were successfully fabricated as free-standing anode materials for lithium ion batteries (LIBs). CuCoNi-oxide nanowire arrays could provide more active sites owing to the hyperbranched structure, leading to a better specific capacity of 1191 mAh/g, cycle performance of 73% retention in comparison to CuO nanowire structure, which exhibited a specific capacity of 1029 mAh/g and capacity retention of 43%, respectively.