An Efficient Halogen‐Free Electrolyte for Use in Rechargeable Magnesium Batteries

Abstract

Unlocking the full potential of rechargeable magnesium batteries has been partially hindered by the reliance on chloride-based complex systems.D espite the high anodic stability of these electrolytes,they are corrosive towardmetallic battery components,which reduce their practical electrochemical window. Following on our new design concept involving boron cluster anions,m onocarborane CB 11 H 12 À produced the first halogen-free,s imple-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(CB 11 H 12 ) 2 /tetraglyme (MMC/G4) electrolyte system permits standardized methods of high-voltage cathode testing that uses atypical coin cell. This achievement is aturning point in the researcha nd development of Mg electrolytes that has deep implications on realizing practical rechargeable Mg batteries.Currently,the prospect of attaining energy densities beyond those offered by current lithium-ion batteries is driving interest in rechargeable magnesium batteries.M gm etal offers high volumetric capacity (3833 mAh cm À3 vs. 2036 mAh cm À3 for Li metal) while being non-dendritic and abundant in the earth crust (fifth most abundant element). [1] Since Aurbach et al. demonstrated the first and only rechargeable Mg battery prototype,c hallenges toward realizing Mg batteries still remain. [2] These stem from the absence of practical electrolytes and high capacity/high voltage cathodes. Fori nstance,t he field demands electrolytes capable of operating at high voltages whilst being compatible with Mg metal and all other battery components. [3]

Electrolytes for Batteries with Earth‐Abundant Metal Anodes

“…[41][42][43] These studies showed that modified structures would lead to high magnesium plating efficiencies with higher potential windows. After the first introduction of ar eversible magnesium battery,m any studies concerning magnesium organoaluminates and organoborates have been reported.…”

Mg Cathode Materials and Electrolytes for Rechargeable Mg Batteries: A Review

“…Electrolytes of Mg organoborate salts containing boratecentred anions were recently reported to support reversible Mg plating and stripping. [39][40][41] Cui's group reported functional electrolytes comprising of bulky organoborate anions with fully fluorine-substituted propoxide chains. [41] With the addition of tris(2H-hexafluoroisopropyl) borate (THFPB), MgF 2 salt was partially dissolved in DME, to generate the anion and cationic species [FTHB] À and [Mg(DME) n ] 2 + respectively (Figure 7a and 7b).…”

“…Recently the same group also reported a novel magnesium electrolyte comprising of [B(HFIP) 4 ] À anion couple with a solvated [Mg 4 Cl 6 (DME) 6 4 ] and MgBr 2 in DME, forming highly conductive electrolytes (6.8 mS cm À1 ). [39] These electrolytes showed high anodic stability, especially on a stainless steel (SS) electrode (up to 4.3 V vs Mg). For the anion, since each boron centre is bonded to four oxygens from the fluorinated propoxide, electrons are well-delocalized from the electron-rich BÀO bonds through the adjacent electron-withdrawing fluorinated group.…”

“…Mg/S batteries have also been studied recently. [19,20,[39][40][41]127,128] The initial active cathode material is S 8 , and a non-nucleophilic environment is needed to avoid reaction with the cathode. Most effective Mg electrolytes, such as Grignard-based systems; or Mg organohaloaluminate electrolytes, contain nucleophilic groups such as ethyl, butyl, or phenyl, which are reactive with electrophilic sulfur.…”

Rechargeable Aluminum/Iodine Battery Redox Chemistry in Ionic Liquid Electrolyte

“…[1][2][3][4][5][6][7][8][9] Rechargeable aluminum ion batteries (RABs) have been considered one of the most promising next-generation rechargeable battery because Al is the most abundant metal element in earth's crust, and it can provide a remarkable volumetric capacity (8.05 Ahcm -3 ), which is four times higher than that of lithium.…”