Investigation of Ca Insertion into α-MoO3 Nanoparticles for High Capacity Ca-Ion Cathodes

Self-Adaptive Electrochemistry of Phosphate Cathodes toward Improved Calcium Storage

Polyanion phosphates exhibit great potential as calcium-ion battery (CIB) cathodes, boasting high working voltage and rapid ion diffusion. Nevertheless, they frequently suffer from capacity decay with irreversible phase transitions; the underlying mechanisms remain elusive. Herein, we report an adaptively layerized structure evolution from discrete NaV2O2(PO4)2F nanoparticles (NPs) to interconnected VOPO4 nanosheets (NSs), triggered by electrochemical (de)calcification, leading to an improvement in Ca2+ storage performance. This electrochemistry-driven self-adapted layerization occurs over approximately 200 cycles, during which NPs undergo a "deform/merge-layerization" process, transitioning from a three-dimensional to a two-dimensional atomic structure, with a distinct 0.68 nm lattice spacing. The transition mechanism is demonstrated to be linked to the gradual separation of structural Na+ and F-. The resultant VOPO4 NSs exhibit exceptional Ca2+ diffusion kinetics (3.19 × 10-9 cm2 s-1, currently the optimal value among inorganic cathode materials for CIBs), enhanced capacity (∼100 mA h g-1), longevity (over 1000 cycles at 50 mA g-1), and high rate (84% retention rates when increasing current density from 50 to 200 mA g-1). Employing advanced electron microscopy, this study reveals an electrochemical activation-induced structure evolution at the atomic level, providing valuable insights into the design of high-performance CIB cathodes.

Cathode materials for non-aqueous calcium rechargeable batteries

Calcium rechargeable batteries based on divalent charge carriers have the potential to meet the future demands for large-scale energy storage applications, due to the crustal abundance of Ca element and the high capacity and high safety of Ca metal anodes. The discernible progress in electrolyte and anode materials has put calcium battery technology a step closer to practice. However, the pursuit of high-voltage, high-capacity and stable cathode materials had been formidable because of the sluggish ion migration kinetics and the instability of host lattices during Ca2+ insertion and extraction. Unlocking the potential of Ca rechargeable batteries particularly hinges on the strategic identification of high-performance cathode materials. Herein, this review summarizes the representative strategies to develop novel cathode materials that allow reversible accommodation of Ca2+ ions for high energy output. The cathode materials can be classified into intercalation-type (layered structure, polyanionic compounds, and Prussian blue analogues) and conversion-type (organic materials, sulfur, and oxygen). The scrutinization of their performances and drawbacks sheds light on the current stage of cathode material advancement and provides informative suggestions for future studies to develop advanced calcium rechargeable batteries with competitive performance.

Imaging Anisotropic Proton Intercalation in Photochromic MoO3

Protonation represents a fundamental chemical process with promising applications in the fields of energy, environment, and memory devices. Probing the protonation mechanism, however, presents a formidable challenge owing to the elusiveness of intercalated protons. In this work, we utilize the atomic and electronic structure changes associated with protonation to directly image the proton intercalation pathways in α-MoO3 induced by UV illumination. We reveal the anisotropic intercalation behavior which is initiated by photocatalyzed water dissociation preferentially at the (001) edges and then propagates along the c axis, transforming α-MoO3 into HxMoO3 to realize photochromism. This photochromic process can be reversed via heating in air, leading to anisotropic proton deintercalation, also preferentially along the c axis. The observed anisotropic behavior can be attributed to the intrinsically low energy barriers for both proton migration along the c axis and water dissociation/formation at (001) edges.

Intercalating a potassium-aqua complex cation into an α-MoO3 layer without reducing molybdenum: a potential storage system

We have demonstrated a green aqueous synthesis of rod-shaped MoO3 material, [MoVI3O9{K(H2O)4}(CH3COO)]·H2O (2) intercalating potassium-aqua-complex acetate into its lamellar space, simply by ion-exchange of Co(II)-aqua-complex in compound [MoVI4O12(CH3COO)2{CoII(H2O)6}]·2H2O (1) by {K(H2O)4}+ in an aqueous solution of 1 and KCl. Compound 2 acts as a potential storage system of alkali metal ions.

A rechargeable Ca/Cl2 battery

Rechargeable calcium (Ca) metal batteries are promising candidates for sustainable energy storage due to the abundance of Ca in Earth's crust and the advantageous theoretical capacity and voltage of these batteries. However, the development of practical Ca metal batteries has been severely hampered by the current cathode chemistries, which limit the available energy and power densities, as well as their insufficient capacity retention and low-temperature capability. Here, we describe the rechargeable Ca/Cl2 battery based on a reversible cathode redox reaction between CaCl2 and Cl2, which is enabled by the use of lithium difluoro(oxalate)borate as a key electrolyte mediator to facilitate the dissociation and distribution of Cl-based species and Ca2+. Our rechargeable Ca/Cl2 battery can deliver discharge voltages of 3 V and exhibits remarkable specific capacity (1000 mAh g-1) and rate capability (500 mA g-1). In addition, the excellent capacity retention (96.5% after 30 days) and low-temperature capability (down to 0 °C) allow us to overcome the long-standing bottleneck of rechargeable Ca metal batteries.

Adsorption of Ca on borophene for potential anode for Ca-ion batteries

CONTEXT

Two-dimensional borophene can be used in rechargeable batteries due to its high specific surface area. In this paper, the performance of borophene as an anode material for calcium ion batteries is predicted based on density functional theory calculations. The calculation results show that P doping enhances the calcium storage properties of borophene. The maximum adsorption number of calcium atoms in the P-doped system is 7, with a theoretical capacity of 964 mAh/g. DOS analysis showed that borophene exhibited metallic properties after adsorbing calcium atoms, which improved the electrical conductivity of the electrode material. Calculation of the diffusion energy barrier shows that strain has an effect on calcium diffusion in monolayer borophene, and compressive strain promotes calcium diffusion through borophene. The findings suggest that borophene may be a promising electrode material for calcium-ion batteries.

METHODS

In this paper, the intrinsic model and doping model of borophene are constructed by Material Studio 8.0, and the first-principles calculation is carried out by CASTEP module.