Catalyzing Desolvation at Cathode-Electrolyte Interface Enabling High-Performance Magnesium-Ion Batteries.

Magnesium ion batteries (MIBs) are expected to be the promising candidates in the post-lithium-ion era with high safety, low cost and almost dendrite-free nature. However, the sluggish diffusion kinetics and strong solvation capability of the strongly polarized Mg2+ are seriously limiting the specific capacity and lifespan of MIBs. In this work, catalytic desolvation is introduced into MIBs for the first time by modifying vanadium pentoxide (V2 O5 ) with molybdenum disulfide quantum dots (MQDs), and it is demonstrated via density function theory (DFT) calculations that MQDs can effectively lower the desolvation energy barrier of Mg2+ , and therefore catalyze the dissociation of Mg2+ -1,2-Dimethoxyethane (Mg2+ -DME) bonds and release free electrolyte cations, finally contributing to a fast diffusion kinetics within the cathode. Meanwhile, the local interlayer expansion can also increase the layer spacing of V2 O5 and speed up the magnesiation/demagnesiation kinetics. Benefiting from the structural configuration, MIBs exhibit superb reversible capacity (≈300 mAh g-1 at 50 mA g-1 ) and unparalleled cycling stability (15 000 cycles at 2 A g-1 with a capacity of ≈70 mAh g-1 ). This approach based on catalytic reactions to regulate the desolvation behavior of the whole interface provides a new idea and reference for the development of high-performance MIBs.

Organic Molecular Intercalation Enabled Anionic Redox Chemistry with Fast Kinetics for High Performance Magnesium Storage.

Rechargeable magnesium-ion batteries possess desirable characteristics in large-scale energy storage applications. However, severe polarization, sluggish kinetics and structural instability caused by high charge density Mg2+ hinder the development of high-performance cathode materials. Herein, the anionic redox chemistry in VS4 is successfully activated by inducing cations reduction and introducing anionic vacancies via polyacrylonitrile (PAN) intercalation. Increased interlayer spacing and structural vacancies can promote the electrolyte ions migration and accelerate the reaction kinetics. Thanks to this "three birds with one stone" strategy, PAN intercalated VS4 exhibits an outstanding electrochemical performance: high discharge specific capacity of 187.2 mAh g-1 at 200 mA g-1 after stabilization and a long lifespan of 5000 cycles at 2 A g-1 are achieved, outperforming other reported VS4-based materials to date for magnesium storage under the APC electrolyte. Theoretical calculations confirm that the intercalated PAN can indeed induce cations reduction and generate anionic vacancies by promoting electron transfer, which can accelerate the electrochemical reaction kinetics and activate the anionic redox chemistry, thus improving the magnesium storage performance. This approach of organic molecular intercalation represents a promising guideline for electrode material design on the development of advanced multivalent-ion batteries.

Enabling Ultrafast Single Mg2+ Insertion Kinetics of Magnesium-Ion Batteries via In Situ Dynamic Catalysis and Re-equilibration Effects.

Magnesium-ion batteries (MIBs) have great potential in large-scale energy storage field with high capacity, excellent safety, and low cost. However, the strong solvation effect of Mg2+ will lead to the formation of solvated ions in electrolytes with larger size and sluggish diffusion/reaction kinetics. Here, the concept of interfacial catalytic bond breaking is first introduced into the cathode design of MIBs by hybriding MoS2 quantum dots with VS4 (VS4@MQDs) as the cathode. The "in situ dynamic catalysis and re-equilibration" effects can catalyze the Cl-Mg bond breaking and trigger single Mg2+ insertion/extraction chemistries, which can significantly accelerate the diffusion and reaction kinetics, as verified by the decreased diffusion energy barriers (0.26 eV for Mg2+ vs 2.47 eV for MgCl+) and fast diffusion coefficient. Benefitting from these dynamic catalysis effects, the constructed VS4@MQD-based MIBs deliver a high discharge capacity of ∼120 mA h g-1 at 200 mA g-1 and a long-term cyclic stability of 1000 cycles at 1 A g-1. The improved performance and detailed characterizations well prove that the active ions in MIBs change from MgCl+/Mg2Cl3+ to Mg2+ with fast kinetics.

Magnetic and microwave absorbing properties of low-temperature sintered BaZr x Fe(12-x)O19.

In the present work, to enhance the reflection loss and change the magnetic resonance frequency of barium ferrite sintered at low temperature, different amounts of Zr ion were introduced to BaFe12O19 to substitute the Fe ion. A series of M-type barium hexaferrite samples having the nominal composition BaZr x Fe(12-x)O19 (x = 0.0, 0.3, 0.6, 0.9 and 1.2) was successfully synthesized by heat treatment at a relatively low temperature (900 °C) for 2 h. In order to study the phases, morphologies and magnetic properties of the substituted barium ferrites, X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were used. The XRD patterns indicated that all samples were single phase M-type ferrites. The SEM images showed that all samples were hexagonal-shaped particles and the average size was about 500 nm. Simultaneously, a potassium chloride additive can effectively reduce the sintering temperature of barium ferrites and their formation and morphology are apparently not affected. The VSM results demonstrated that the coercivity steeply decreased from 4772.43 Oe to 797.34 Oe when the Zr ion substitution amount increased from 0.0 to 1.2 but the saturation magnetization remained almost constant (M s = 49.71-63.06 emu g-1). Furthermore, the complex electromagnetic parameters were collected by a vector network analyzer (VNA) and the microwave absorbing properties were calculated according to transmission theory. It was found that the reflection loss is enhanced with increasing x. The minimum reflection loss value of -30.2 dB at 16.75 GHz was observed and the bandwidth is about 2.46 GHz for the x = 1.2 sample. BaZr x Fe(12-x)O19 might be a promising candidate for applications of LTCC (low-temperature co-fired ceramic) substrates for millimeter wave circulators and filters.