Magnesium Insertion in Vanadium Oxides: A Structural Study

A Sustainable Technique to Prepare High-Purity Vanadium Pentoxide via Purification with Low Ammonium Consumption

The general preparation method for V₂O₅ is ammonium salt vanadium precipitation, which inevitably produces large amounts of ammonia nitrogen wastewater. In this paper, we propose an environmentally friendly method for preparing high-purity V₂O₅ with low ammonium consumption. The purity of the V₂O₅ product reaches more than 99% while reducing the level of ammonium consumption. The vanadium precipitation efficiency reaches 99.23% and the V₂O₅ purity of the product reaches 99.05% under the following conditions: precipitation time of 1.5 h, precipitation temperature of 98 °C, initial precipitation pH of 2, ammonium addition coefficient of 2, purification time of 5 min with purification performed twice, purification temperature of 65 °C. In this study, compared with the use of ammonia spirit for vanadium precipitation and ammonium salt vanadium precipitation, the ammonia consumption levels are reduced by 79.80% and 80.00%, and the purity levels are increased by 0.70% and 1.01%, respectively. The compositions of the precipitated (NaV₃O₈∙xH₂O) and purified ((NH₄)₂V₆O₁₆·1.5H₂O) hydrolysis products are characterized via XRD. The TGA results show that NaV₃O₈∙xH₂O contains 1.5 times the amount of crystal water. The FTIR results explain that the two V₃O₈⁻ layers are combined end-to-end to form a V₆O₁₆²⁻ layer. The change of the product image indicates that the purification process includes three stages. Firstly, heating and NH₄⁺ attack expand the V₃O₈⁻ layer. NH4⁺ diffuses more easily into the V₃O₈⁻ layer. Secondly, NH₄⁺ destroys the electrostatic interaction between Na⁺ with the V₃O₈⁻ layer and replacing Na⁺. Finally, V₃O₈⁻ is polymerized into V₆O₁₆²⁻ to keep the crystal structure stable.

Water-Activated VOPO4 for Magnesium Ion Batteries

Rechargeable Mg batteries, using high capacity and dendrite-free Mg metal anodes, are promising energy storage devices for large scale smart grid due to low cost and high safety. However, the performance of Mg batteries is still plagued by the slow reaction kinetics of their cathode materials. Recent discoveries demonstrate that water in cathode can significantly enhance the Mg-ion diffusion in cathode by an unknown mechanism. Here, we propose the water-activated layered-structure VOPO₄ as a novel cathode material and examine the impact of water in electrode or organic electrolyte on the thermodynamics and kinetics of Mg-ion intercalation/deintercalation in cathodes. Electrochemical measurements verify that water in both VOPO₄ lattice and organic electrolyte can largely activate VOPO₄ cathode. Thermodynamic analysis demonstrates that the water in the electrolyte will equilibrate with the structural water in VOPO₄ lattice, and the water activity in the electrolyte alerts the mechanism and kinetics for electrochemical Mg-ion intercalation in VOPO₄. Theoretical calculations and experimental results demonstrate that water reduces both the solid-state diffusion barrier in the VOPO₄ electrode and the desolvation penalty at the interface. To achieve fast reaction kinetics, the water activity in the electrolyte should be larger than 10^-2. The proposed activation mechanism provides guidance for screening and designing novel chemistry for high performance multivalent-ion batteries.

Elucidating Solvation Structures for Rational Design of Multivalent Electrolytes-A Review

Fundamental molecular-level understanding of functional properties of liquid solutions provides an important basis for designing optimized electrolytes for numerous applications. In particular, exhaustive knowledge of solvation structure, stability, and transport properties is critical for developing stable electrolytes for fast-charging and high-energy-density next-generation energy storage systems. Accordingly, there is growing interest in the rational design of electrolytes for beyond lithium-ion systems by tuning the molecular-level interactions of solvate species present in the electrolytes. Here we present a review of the solvation structure of multivalent electrolytes and its impact on the electrochemical performance of these batteries. A direct correlation between solvate species present in the solution and macroscopic properties of electrolytes is sparse for multivalent electrolytes and contradictory results have been reported in the literature. This review aims to illustrate the current understanding, compare results, and highlight future needs and directions to enable the deep understanding needed for the rational design of improved multivalent electrolytes.

Unraveling the Magnesium-Ion Intercalation Mechanism in Vanadium Pentoxide in a Wet Organic Electrolyte by Structural Determination

Magnesium batteries have received attention as a type of post-lithium-ion battery because of their potential advantages in cost and capacity. Among the host candidates for magnesium batteries, orthorhombic α-V₂O₅ is one of the most studied materials, and it shows a reversible magnesium intercalation with a high capacity especially in a wet organic electrolyte. Studies by several groups during the last two decades have demonstrated that water plays some important roles in getting higher capacity. Very recently, proton intercalation was evidenced mainly using nuclear resonance spectroscopy. Nonetheless, the chemical species inserted into the host structure during the reduction reaction are still unclear (i.e., Mg(H₂O)_n²⁺, Mg(solvent, H₂O)_n²⁺, H⁺, H₃O⁺, H₂O, or any combination of these). To characterize the intercalated phase, the crystal structure of the magnesium-inserted phase of α-V₂O₅, electrochemically reduced in 0.5 M Mg(ClO₄)₂ + 2.0 M H₂O in acetonitrile, was solved for the first time by the ab initio method using powder synchrotron X-ray diffraction data. The structure was tripled along the b-axis from that of the pristine V₂O₅ structure. No appreciable densities of elements were observed other than vanadium and oxygen atoms in the electron density maps, suggesting that the inserted species have very low occupancies in the three large cavity sites of the structure. Examination of the interatomic distances around the cavity sites suggested that H₂O, H₃O⁺, or solvated magnesium ions are too big for the cavities, leading us to confirm that the intercalated species are single Mg²⁺ ions or protons. The general formula of magnesium-inserted V₂O₅ is Mg_0.17H_xV₂O₅, (0.66 ≤ x ≤ 1.16). Finally, density functional theory calculations were carried out to locate the most plausible atomic sites of the magnesium and protons, enabling us to complete the structure modeling. This work provides an explicit answer to the question about Mg intercalation into α-V₂O₅.

Mapping the Challenges of Magnesium Battery

Rechargeable Mg battery has been considered a major candidate as a beyond lithium ion battery technology, which is apparent through the tremendous works done in the field over the past decades. The challenges for realization of Mg battery are complicated, multidisciplinary, and the tremendous work done to overcome these challenges is very hard to organize in a regular review paper. Additionally, we claim that organization of the huge amount of information accumulated by the great scientific progress achieved by various groups in the field will shed the light on the unexplored research domains and give clear perspectives and guidelines for next breakthrough to take place. In this Perspective, we provide a convenient map of Mg battery research in a form of radar chart of Mg electrolytes, which evaluates the electrolyte under the important components of Mg batteries. The presented radar charts visualize the accumulated knowledge on Mg battery and allow for navigation of not only the current research state but also future perspective of Mg battery at a glance.

A Brief Review on Multivalent Intercalation Batteries with Aqueous Electrolytes

Rapidly growing global demand for high energy density rechargeable batteries has driven the research toward developing new chemistries and battery systems beyond Li-ion batteries. Due to the advantages of delivering more than one electron and giving more charge capacity, the multivalent systems have gained considerable attention. At the same time, affordability, ease of fabrication and safety aspects have also directed researchers to focus on aqueous electrolyte based multivalent intercalation batteries. There have been a decent number of publications disclosing capabilities and challenges of several multivalent battery systems in aqueous electrolytes, and while considering an increasing interest in this area, here, we present a brief overview of their recent progress, including electrode chemistries, functionalities and challenges.

Theoretical study on the initial stage of a magnesium battery based on a V2O5 cathode

The barrierless α to δ phase transformation is proposed as a possible explanation for the full reversibility of a Mg battery with a V₂O₅ cathode.

Tailoring insoluble nanobelts into soluble anti-UV nanopotpourris

Soluble, transparent and anti-UV nanopotpourris have been prepared by tailoring long nanobelts. The strains and layered structures facilitate the breaking of the as-synthesized nanobelts under an applied mechanical action. The developed tailoring process of nanobelts is a general top-down secondary processing of layered nanostructures at the nanoscale level, which can be expended to the modifications of layered nanowires, nanotubes and hierarchical nanostructures. By tailoring, the size, morphology and solubility are modified, which may open up an area of advanced processing of nanomaterials and hint at some potential applications. Because of the excellent solubility of the tailored nanopotpourris, they are easily dispersed in cosmetics or polymer films, which are quite useful for some anti-UV protection applications, such as anti-UV sunscreen creams and anti-UV window films for vehicles and buildings.