Cosolvent‐Assisted Formation of Charged Ion‐Solvent Clusters and Solid Electrolyte Interphase for High‐Performance Magnesium Metal Batteries

Abstract

High‐performance magnesium electrolyte is crucial for the practical application of rechargeable Mg batteries. Herein, a bis(2,2,2‐trifluoroethyl) ether (BTFE) cosolvent is introduced into the chlorine‐containing Mg electrolytes. Theoretical calculations and experimental characterizations reveal that the positive electrostatic potential distributed around the hydrogen atoms in a BTFE molecule could interact with Cl− and facilitate the formation of charged, instead of neutral, ion‐solvent clusters in the BTFE cosolvated magnesium lithium chloride complex (MLCC) electrolyte, which helps to lift its ionic conductivity. The modified solvation structure also lowers the lowest unoccupied molecular orbital energy level of the ion‐solvent clusters, facilitating the in situ formation of solid electrolyte interphase. Using the BTFE cosolvated MLCC electrolyte, reversible Mg plating/stripping can be achieved at 20 mA cm−2 in a Mg//Mg cell, and an ultra‐long cycle life of 1200 h can be achieved at 5 mA cm−2. The new electrolyte also enables high capacity retention of 160 mAh g−1 after 800 cycles for a Mg//CuS full cell, or super‐long cycle life of over 10 000 cycles at 80 C for a Mg//Mo6S8 full cell. The merits of BTFE cosolvent, universally applicable to other chlorine‐containing Mg electrolytes, open a way to develop practical Mg battery electrolytes.

Magnesium Battery Electrolytes with Improved Oxidative Stability Enabled by Selective Solvation in Fluorinated Solvents

“…While there are many reported examples of HFE-based electrolytes for alkali metal batteries, − such electrolytes have scarcely been applied to Mg batteries. To our knowledge, the single reported example utilized high Cl – anion and Li + cation concentrations, which preclude the application of high voltage Mg 2+ cathodes . In contrast, our strategy aims at maximizing overall oxidative stability in the absence of additives that would inhibit cathode function.…”

“…To our knowledge, the single reported example utilized high Cl − anion and Li + cation concentrations, which preclude the application of high voltage Mg 2+ cathodes. 17 In contrast, our strategy aims at maximizing overall oxidative stability in the absence of additives that would inhibit cathode function. This strategy takes advantage of two unique characteristics of the HFE solvent class imparted by electron withdrawal from the ether oxygen by the electronegative fluorine atoms: high oxidative stability and weak coordination strength.…”

Revealing the Interfacial Chemistry of Fluoride Alkyl Magnesium Salts in Magnesium Metal Batteries

“…For Mg anode cycled in MPFB electrolyte, the C=O (532.5 eV) attributable to the solvent decomposition is observed before sputtering, and then the oxide peaks (529.9 eV) gradually dominate (Figure 4a). [32] It is worth mentioning that the cell disassembly and XPS samples preparation were carried out in an argon-filled glove box, so the interference of oxygen in the air can be excluded. Then, the Cl 2p XPS spectra (198.6 eV and 202.2 eV) were present throughout the sputtering process suggesting the vertical homogeneous distribution of chlorides (Figure 4e).…”

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

“…To realize the carbon peaking and carbon neutrality on schedule, development of large-scale sustainable energy storage technologies is significantly important nowadays. Rechargeable magnesium-ion batteries (MIBs) have emerged as the most favorable candidates in the era of post-lithium-ion batteries (LIBs) due to their low reduction potential (−2.37 V vs SHE), high volumetric capacity (3883 mA h cm –3 ), abundant reserves, and cost-effectiveness. − Most importantly, the essentially dendrite-free property of magnesium during electrochemical Mg 2+ plating has aroused intensive attention from all over the world, − which can create high intrinsic safety batteries . However, a strong electrostatic interaction between divalent Mg 2+ ions and cathode lattices directly affects its intercalation kinetics, which seriously restricts the specific capacity and rate capability of the cathode materials. − Another bottleneck challenge is the strong solvation ability of Mg 2+ , which will tightly interact with solvent molecules to form solvated ions with larger radius size.…”