Paving the Way towards Highly Stable and Practical Electrolytes for Rechargeable Magnesium Batteries

Despite being considered a promising anode candidate for future battery technologies, the reactivity of Mg metal and its resultant passivation have challenged the development of electrolytes for rechargeable Mg batteries. In this Concept article, we shed light on critical past and current motivations, hurdles, and design strategies of electrolyte development for Mg batteries. Special focus is given to the most recent advancements; in particular, we elaborate on bottom‐up design strategies targeted to overcome the corrosion issue caused by current electrolyte systems. Salts containing the BH motif expanded the portfolio of Mg‐compatible electrolytes and are used as a platform to create a whole new promising family. Here, we explain the approach, challenges, and the path forward for ultimately creating Mg‐compatible, highly stable, and non‐corrosive Mg electrolytes.Enhancing electrolytes: A platform to design electrolytes for rechargeable Mg batteries based on the BH motif has generated a new family of highly promising and noncorrosive electrolytes. The principles that guided the design of state‐of‐the‐art Mg electrolytes and their properties are discussed. In addition, a bottom‐up design approach based on BH compounds is described.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110620/1/celc_201402207_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110620/2/51_ftp.pd

Magnesium Borohydride: From Hydrogen Storage to Magnesium Battery

Beyond hydrogen storage: The first example of reversible magnesium deposition/stripping onto/from an inorganic salt was seen for a magnesium borohydride electrolyte. High coulombic efficiency of up to 94 % was achieved in dimethoxyethane solvent. This Mg(BH_4)_2 electrolyte was utilized in a rechargeable magnesium battery

Magnesium-Sodium Hybrid Battery With High Voltage, Capacity and Cyclability

Rechargeable magnesium battery has been widely considered as a potential alternative to current Li-ion technology. However, the lack of appropriate cathode with high-energy density and good sustainability hinders the realization of competitive magnesium cells. Recently, a new concept of hybrid battery coupling metal magnesium anode with a cathode undergoing the electrochemical cycling of a secondary ion has received increased attention. Mg-Na hybrid battery, for example, utilizes the dendritic-free deposition of magnesium at the anode and fast Na+-intercalation at the cathode to reversibly store and harvest energy. In the current work, the principles that take the full advantage of metal Mg anode and Na-battery cathode to construct high-performance Mg-Na hybrid battery are described. By rationally applying such design principle, we constructed a Mg-NaCrO2 hybrid battery using metal Mg anode, NaCrO2 cathode and a mixture of all-phenyl complex (PhMgCl-AlCl3, Mg-APC) and sodium carba-closo-dodecaborate (NaCB11H12) as dual-salt electrolyte. The Mg-NaCrO2 cell delivered an energy density of 183 Wh kg−1 at the voltage of 2.3 V averaged in 50 cycles. We found that the amount of electrolyte can be reduced by using solid MgCl2 as additional magnesium reservoir while maintaining comparable electrochemical performance. A hypothetical MgCl2-NaCrO2 hybrid battery is therefore proposed with energy density estimated to be 215 Wh kg−1 and the output voltage over 2 V

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.A simple yet multifaceted magnesium monocarborane (MMC) based electrolyte was prepared. This remarkable halogen‐free and benign system is compatible with Mg metal and displays the highest anodic stability reported to date. The non‐corrosive nature of the MMC electrolyte enabled the examination of high‐voltage cathodes in a coin cell, which is a critical step forward in realizing practical rechargeable Mg batteries.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111923/1/anie_201412202_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/111923/2/7900_ftp.pd

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.Ein einfacher und doch vielfältiger Magnesiummonocarboran(MMC)‐basierter Elektrolyt als bemerkenswertes halogenfreies und umweltschonendes System ist mit Mg‐Metall kompatibel und weist die bislang höchste anodische Stabilität auf. Wegen seiner nichtkorrodierenden Art ermöglicht der MMC‐Elektrolyt die Untersuchung von Hochspannungskathoden in einer Knopfzelle – ein wichtiger Schritt hin zu praktisch einsetzbaren wiederaufladbaren Mg‐Batterien.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111952/1/8011_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/111952/2/ange_201412202_sm_miscellaneous_information.pd

Synthesis, Characterization, and Atomistic Modeling of Stabilized Highly Pyrophoric Al(BH_4)_3 via the Formation of the Hypersalt K[Al(BH_4)_4]

The recent discovery of a new class of negative ions called hyperhalogens allows us to characterize this complex as belonging to a unique class of materials called hypersalts. Hyperhalogen materials are important while serving as the building blocks for the development of new materials having enhanced magnetic or oxidative properties. One prime example of a hydperhalogen is the Al(BH_4)_4^– anion. Aluminum borohydride (17 wt % H) in itself is a volatile, pyrophoric compound that has a tendency to release diborane at room temperature, making its handling difficult and very undesirable for use in practical applications. Here we report that the combination of Al(BH_4)_3 with the alkaline metal borohydride KBH_4 results in the formation of a new compound KAl(BH_4)_4 which is a white solid that exhibits remarkable thermal stability up to 154 °C and has the typical makeup of a hypersalt material. Using a variety of characterization tools and theoretical calculations, we study and analyze the physical characteristics of this compound and show its potential for stabilizing high hydrogen capacity, energetic materials

Metallic and complex hydride-based electrochemical storage of energy

The development of efficient storage systems is one of the keys to the success of the energy transition. There are many ways to store energy, but among them, electrochemical storage is particularly valuable because it can store electrons produced by renewable energies with a very good efficiency. However, the solutions currently available on the market remain unsuitable in terms of storage capacity, recharging kinetics, durability, and cost. Technological breakthroughs are therefore expected to meet the growing need for energy storage. Within the framework of the Hydrogen Technology Collaboration Program—H2TCP Task-40, IEA\u27s expert researchers have developed innovative materials based on hydrides (metallic or complex) offering new solutions in the field of solid electrolytes and anodes for alkaline and ionic batteries. This review presents the state of the art of research in this field, from the most fundamental aspects to the applications in battery prototypes

Metallic and complex hydride-based electrochemical storage of energy

The development of efficient storage systems is one of the keys to the success of the energy transition. There are many ways to store energy, but among them, electrochemical storage is particularly valuable because it can store electrons produced by renewable energies with a very good efficiency. However, the solutions currently available on the market remain unsuitable in terms of storage capacity, recharging kinetics, durability, and cost. Technological breakthroughs are therefore expected to meet the growing need for energy storage. Within the framework of the Hydrogen Technology Collaboration Program - H2TCP Task-40, IEA's expert researchers have developed innovative materials based on hydrides (metallic or complex) offering new solutions in the field of solid electrolytes and anodes for alkaline and ionic batteries. This review presents the state of the art of research in this field, from the most fundamental aspects to the applications in battery prototypes

Beyond Typical Electrolytes for Energy Dense Batteries

The ever-rising demands for energy dense electrochemical storage systems have been driving interests in beyond Li-ion batteries such as those based on lithium and magnesium metals. These high energy density batteries suffer from several challenges, several of which stem from the flammability/volatility of the electrolytes and/or instability of the electrolytes with either the negative, positive electrode or both. Recently, hydride-based electrolytes have been paving the way towards overcoming these issues. Namely, highly performing solid-state electrolytes have been reported and several key challenges in multivalent batteries were overcome. In this review, the classes of hydride-based electrolytes reported for energy dense batteries are discussed. Future perspectives are presented to guide research directions in this field