Salt-in-Salt Mediated Weak-Solvent Electrolyte Enabling Fast-Charging and Wide-Temperature Lithium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Conventional electrolytes limit spinel LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ (LNMO) cathode applications due to poor high-voltage stability, slow ion transport, and unstable interphases.
• Weakly solvating electrolytes (WSEs) offer potential but face challenges in oxidation resistance and kinetics.

Purpose of the Study:

• To develop advanced electrolytes for LNMO cathodes enabling fast-charging and wide-temperature performance.
• To overcome limitations of conventional and existing WSEs through a novel salt-in-salt strategy.

Main Methods:

• A "strong-weak synergy" strategy using fluorinated WSEs mediated by Mg(TFSI)$_{2}$ and MgF$_{2}$.
• Harnessing Mg$^{2+}$ Lewis acidity to control LiDFOB dissociation and Li$^{+}$ desolvation.
• Directing inorganic cathode-electrolyte interphase (CEI) formation via Mg$^{2+}$ interaction with interfacial anions.

Main Results:

• The developed electrolyte enables exceptional fast-charging and cycling stability for LNMO||Li cells from -30 to 70°C.
• Pouch cells demonstrated 88.9% capacity retention after 400 cycles.
• The electrolyte is non-flammable and compatible with various high-nickel and olivine-type cathodes.

Conclusions:

• The dual-regulation mechanism optimizes bulk ion conduction and interfacial stability, addressing WSE limitations.
• This work provides insights into solvation chemistry and interfacial engineering for safer, high-performance lithium-ion batteries.
• The strategy shows broad applicability for advanced lithium-ion battery chemistries.