An Efficient Halogen-Free Electrolyte for Use in Rechargeable Magnesium Batteries.

Unlocking the full potential of rechargeable magnesium batteries has been partially hindered by the reliance on chloride-based complex systems. Despite the high anodic stability of these electrolytes, they are corrosive toward metallic battery components, which reduce their practical electrochemical window. Following on our new design concept involving boron cluster anions, monocarborane CB11H12(-) produced the first halogen-free, simple-type Mg salt that is compatible with Mg metal and displays an oxidative stability surpassing that of ether solvents. Owing to its inertness and non-corrosive nature, the Mg(CB11H12)2/tetraglyme (MMC/G4) electrolyte system permits standardized methods of high-voltage cathode testing that uses a typical coin cell. This achievement is a turning point in the research and development of Mg electrolytes that has deep implications on realizing practical rechargeable Mg batteries.

Boron-doped graphene as a promising anode for Na-ion batteries.

The Na-ion battery has recently gained a lot of interest as a low-cost alternative to the current Li-ion battery technology. Its feasibility strongly depends on the development of suitable electrode materials. In the present work we propose a novel anode candidate, boron-doped graphene, for the Na-ion battery. Our first-principles calculations demonstrate that the sodiation of boron-doped graphene well preserves its structural integrity. The 2D-BC3 anode has the average sodiation voltage of 0.44 V in an appropriate range to avoid the safety concerns caused by the formation of dendritic deposits. The capacity of the 2D-BC3 anode reaches ∼2.04 times that of the graphite anode in a Li-ion battery and ∼2.52 times that of hard carbon in a Na-ion battery. The high electronic mobility and Na mobility on boron-doped graphene indicates that it has a high potential to reach good rate performance. These suggest the promising potential of boron-doped graphene to serve as an anode for a rechargeable Na-ion battery.

Boron clusters as highly stable magnesium-battery electrolytes.

Boron clusters are proposed as a new concept for the design of magnesium-battery electrolytes that are magnesium-battery-compatible, highly stable, and noncorrosive. A novel carborane-based electrolyte incorporating an unprecedented magnesium-centered complex anion is reported and shown to perform well as a magnesium-battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium-battery electrolytes is very high.

Atomic-Scale Observations of Oxygen Release Degradation in Sulfide-Based All-Solid-State Batteries with Layered Oxide Cathodes.

All-solid-state batteries exhibit considerable potential for applications in electric vehicles. Understanding and controlling the oxygen release from the layered cathode active material are essential in achieving long-term operation of all-solid-state batteries because the oxygen release degrades the cathode material and the solid electrolyte, triggering capacity degradation. In this study, we verified the specific interface where the oxygen release is accelerated by atomic-scale scanning transmission electron microscopy and electron energy loss spectroscopy analyses. Oxygen release is suppressed at the interface where the LiNbO3 coating layer is sufficiently formed. Decomposition products on the solid electrolyte and the antisite defect layers on the cathode surface are formed by oxygen release at the interface where the Li2S-P2S5 solid electrolyte and Li(Ni1/3Mn1/3Ni1/3)O2 cathode are in direct contact. These irreversible passivation layers lead to capacity degradation. In addition, we found that exfoliation of the LiNbO3 coating from the cathode not only physically breaks the Li conduction path but also results in oxygen release and the deterioration of the cathode. These atomic-scale insights can further advance the development of all-solid-state batteries by suppressing oxygen release.

Non-Aqueous Primary Li-Air Flow Battery and Optimization of its Cathode through Experiment and Modeling.

A primary Li-air battery has been developed with a flowing Li-ion free ionic liquid as the recyclable electrolyte, boosting power capability by promoting superoxide diffusion and enhancing discharge capacity through separately stored discharge products. Experimental and computational tools are used to analyze the cathode properties, leading to a set of parameters that improve the discharge current density of the non-aqueous Li-air flow battery. The structure and configuration of the cathode gas diffusion layers (GDLs) are systematically modified by using different levels of hot pressing and the presence or absence of a microporous layer (MPL). These experiments reveal that the use of thinner but denser MPLs is key for performance optimization; indeed, this leads to an improvement in discharge current density. Also, computational results indicate that the extent of electrolyte immersion and porosity of the cathode can be optimized to achieve higher current density.

Quantitatively Predict the Potential of MnO2 Polymorphs as Magnesium Battery Cathodes.

Despite tremendous efforts denoted to magnesium battery research, the realization of magnesium battery is still challenged by the lack of cathode candidate with high energy density, rate capability and good recyclability. This situation can be largely attributed to the failure to achieve sustainable magnesium intercalation chemistry. In current work we explored the magnesiation of distinct MnO2 polymorphs using first-principles calculations, focusing on providing quantitative analysis about the feasibility of magnesium intercalation. Consistent with experimental observations, we predicted that ramsdellite-MnO2 and α-MnO2 are conversion-type cathodes while nanosized spinel-MnO2 and MnO2 isostructual to CaFe2O4 are better candidates for Mg intercalation. Key properties that restrict Mg intercalation include not only sluggish Mg migration but also stronger distortion that damages structure integrity and undesirable conversion reaction. We demonstrate that by evaluating the reaction free energy, structural deformation associated with the insertion of magnesium, and the diffusion barriers, a quantitative evaluation about the feasibility of magnesium intercalation can be well established. Although our current work focuses on the study of MnO2 polymorphs, the same evaluation can be applied to other cathode candidates, thus paving the road to identify better cathode candidates in future.

A highly efficient Li2O2 oxidation system in Li-O2 batteries.

A novel indirect charging system that uses a redox mediator was demonstrated for Li-O2 batteries. 4-Methoxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl (MeO-TEMPO) was applied as a mediator to enable the oxidation of Li2O2, even though Li2O2 is electrochemically isolated. This system promotes the oxidation of Li2O2 without parasitic reactions attributed to electrochemical charging and reduces the charging time.

Fullerenes: non-transition metal clusters as rechargeable magnesium battery cathodes.

We discovered that non-transition metal clusters have great potential as rechargeable Mg battery cathodes. Fullerene (C60), one of the prototype materials, was discharged and recharged with a remarkable rate capability. This unique rate performance is attributed to its capability to delocalize electrons on the entire cluster rather than to individual atoms.

A conceptual magnesium battery with ultrahigh rate capability.

A new type of rechargeable Mg battery is demonstrated, which achieves charge transfer through simultaneous transport of Mg(2+) cations and halogen anions during electrochemical cycling. The novel Mg/AgCl battery shows remarkable rate capability up to 10 C and excellent cyclability at high rates, with a flat plateau at 2 V.

Amorphous V2O5-P2O5 as high-voltage cathodes for magnesium batteries.

A deep investigation of amorphous V2O5-P2O5 powders for magnesium batteries communicates the vital properties to achieving the superior electrochemical performance at a 75 : 25 V2O5 : P2O5 molar ratio. The manipulation of the inter-layer spacing and amorphization of V2O5 can enhance Mg(2+) diffusion and afford a cathode with high-voltage reversibility.

Magnesium batteries: Current state of the art, issues and future perspectives.

"...each metal has a certain power, which is different from metal to metal, of setting the electric fluid in motion..." Count Alessandro Volta. Inspired by the first rechargeable magnesium battery prototype at the dawn of the 21st century, several research groups have embarked on a quest to realize its full potential. Despite the technical accomplishments made thus far, challenges, on the material level, hamper the realization of a practical rechargeable magnesium battery. These are marked by the absence of practical cathodes, appropriate electrolytes and extremely sluggish reaction kinetics. Over the past few years, an increased interest in this technology has resulted in new promising materials and innovative approaches aiming to overcome the existing hurdles. Nonetheless, the current challenges call for further dedicated research efforts encompassing fundamental understanding of the core components and how they interact with each other to offering new innovative solutions. In this review, we seek to highlight the most recent developments made and offer our perspectives on how to overcome some of the remaining challenges.

Understanding the electrochemical mechanism of K-αMnO2 for magnesium battery cathodes.

Batteries based on magnesium are an interesting alternative to current state-of-the-art lithium-ion systems; however, high-energy-density cathodes are needed for further development. Here we utilize TEM, EDS, and EELS in addition to soft-XAS to determine electrochemical magnesiation mechanism of a high-energy density cathode, K-αMnO2. Rather than following the typical insertion mechanism similar to Li(+), we propose the gradual reduction of K-αMnO2 to form Mn2O3 then MnO at the interface of the cathode and electrolyte, finally resulting in the formation of K-αMnO2@(Mg,Mn)O core-shell product after discharge of the battery. Understanding the mechanism is a vital guide for future magnesium battery cathodes.

A high energy-density tin anode for rechargeable magnesium-ion batteries.

A high energy-density Sn anode capable of displaying superior operating voltages and capacity, for rechargeable Mg-ion batteries, is highlighted. The intended application and performance of the anode is confirmed by coupling it with a Mo(6)S(8) cathode in a conventional battery electrolyte.

Quantitation of Li2O2 stored in Li-O2 batteries based on its reaction with an oxoammonium salt.

Precise knowledge of the discharge and charge reactions within Li-O2 batteries is an important aspect of developing highly efficient, rechargeable Li-O2 cells. We describe an analytical method capable of determining the quantity of Li2O2 in the cathode on the basis of the reaction of Li2O2 with an oxoammonium salt.